diff --git a/.gitignore b/.gitignore
index d1a58db5..3c5667f7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -59,3 +59,6 @@ packages/ui/src/icons
 
 # Database
 data/
+
+#IDE
+.idea
diff --git a/packages/api/src/module/shared/commands/uncomplete-task.application-command.ts b/packages/api/src/module/shared/commands/uncomplete-task.application-command.ts
new file mode 100644
index 00000000..ea28dad3
--- /dev/null
+++ b/packages/api/src/module/shared/commands/uncomplete-task.application-command.ts
@@ -0,0 +1,4 @@
+import { UncompleteTask } from '@/commands/uncomplete-task.domain-command';
+import { AbstractApplicationCommand } from '@/module/application-command-events';
+
+export class UncompleteTaskApplicationCommand extends AbstractApplicationCommand<UncompleteTask> {}
diff --git a/packages/api/src/module/shared/commands/uncomplete-task.domain-command.ts b/packages/api/src/module/shared/commands/uncomplete-task.domain-command.ts
new file mode 100644
index 00000000..b0a99c49
--- /dev/null
+++ b/packages/api/src/module/shared/commands/uncomplete-task.domain-command.ts
@@ -0,0 +1,4 @@
+export type UncompleteTask = {
+  type: 'UncompleteTask';
+  data: { learningMaterialsId: string; taskId: string };
+};
diff --git a/packages/api/src/module/write/learning-materials-tasks/application/complete-task.command-handler.ts b/packages/api/src/module/write/learning-materials-tasks/application/complete-task.command-handler.ts
index 3bf718c2..20c74d9a 100644
--- a/packages/api/src/module/write/learning-materials-tasks/application/complete-task.command-handler.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/application/complete-task.command-handler.ts
@@ -2,7 +2,7 @@ import { Inject } from '@nestjs/common';
 import { CommandHandler, ICommandHandler } from '@nestjs/cqrs';
 
 import { CompleteTaskApplicationCommand } from '@/commands/complete-task.application-command';
-import { TaskWasCompleted } from '@/module/events/task-was-completed.domain-event';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
 import { APPLICATION_SERVICE, ApplicationService } from '@/write/shared/application/application-service';
 import { EventStreamName } from '@/write/shared/application/event-stream-name.value-object';
 
@@ -18,7 +18,7 @@ export class CompleteTaskCommandHandler implements ICommandHandler<CompleteTaskA
   async execute(command: CompleteTaskApplicationCommand): Promise<void> {
     const eventStream = EventStreamName.from('LearningMaterialsTasks', command.data.learningMaterialsId);
 
-    await this.applicationService.execute<TaskWasCompleted>(
+    await this.applicationService.execute<LearningMaterialsTasksDomainEvent>(
       eventStream,
       {
         causationId: command.id,
diff --git a/packages/api/src/module/write/learning-materials-tasks/application/uncomplete-task.command-handler.ts b/packages/api/src/module/write/learning-materials-tasks/application/uncomplete-task.command-handler.ts
new file mode 100644
index 00000000..d793717c
--- /dev/null
+++ b/packages/api/src/module/write/learning-materials-tasks/application/uncomplete-task.command-handler.ts
@@ -0,0 +1,29 @@
+import { Inject } from '@nestjs/common';
+import { CommandHandler, ICommandHandler } from '@nestjs/cqrs';
+
+import { UncompleteTaskApplicationCommand } from '@/module/commands/uncomplete-task.application-command';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
+import { uncompleteTask } from '@/write/learning-materials-tasks/domain/uncomplete-task';
+import { APPLICATION_SERVICE, ApplicationService } from '@/write/shared/application/application-service';
+import { EventStreamName } from '@/write/shared/application/event-stream-name.value-object';
+
+@CommandHandler(UncompleteTaskApplicationCommand)
+export class UncompleteTaskCommandHandler implements ICommandHandler<UncompleteTaskApplicationCommand> {
+  constructor(
+    @Inject(APPLICATION_SERVICE)
+    private readonly applicationService: ApplicationService,
+  ) {}
+
+  async execute(command: UncompleteTaskApplicationCommand): Promise<void> {
+    const eventStream = EventStreamName.from('LearningMaterialsTasks', command.data.learningMaterialsId);
+
+    await this.applicationService.execute<LearningMaterialsTasksDomainEvent>(
+      eventStream,
+      {
+        causationId: command.id,
+        correlationId: command.metadata.correlationId,
+      },
+      (pastEvents) => uncompleteTask(pastEvents, command),
+    );
+  }
+}
diff --git a/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.spec.ts b/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.spec.ts
index f9e2e2fe..5c664c72 100644
--- a/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.spec.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.spec.ts
@@ -1,5 +1,7 @@
+import { TaskWasUncompleted } from '@/events/task-was-uncompleted-event.domain-event';
 import { CompleteTask } from '@/module/commands/complete-task.domain-command';
 import { TaskWasCompleted } from '@/module/events/task-was-completed.domain-event';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
 
 import { completeTask } from './complete-task';
 
@@ -61,4 +63,50 @@ describe('complete task', () => {
     // Then
     expect(events).toThrowError('Task was already completed');
   });
+
+  it('should complete uncompleted task', () => {
+    // given
+    const pastEvents: TaskWasUncompleted[] = [
+      {
+        type: 'TaskWasUncompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ];
+
+    // when
+    const events = completeTask(pastEvents, command);
+
+    // then
+    expect(events).toStrictEqual([
+      {
+        type: 'TaskWasCompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ]);
+  });
+
+  it('should complete task if task was completed and then uncompleted', () => {
+    // given
+    const pastEvents: LearningMaterialsTasksDomainEvent[] = [
+      {
+        type: 'TaskWasCompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+      {
+        type: 'TaskWasUncompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ];
+
+    // when
+    const events = completeTask(pastEvents, command);
+
+    // then
+    expect(events).toStrictEqual([
+      {
+        type: 'TaskWasCompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ]);
+  });
 });
diff --git a/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.ts b/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.ts
index 0d03642b..352fa6a9 100644
--- a/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/domain/complete-task.ts
@@ -1,8 +1,9 @@
 import { TaskWasCompleted } from '@/events/task-was-completed.domain-event';
 import { CompleteTask } from '@/module/commands/complete-task.domain-command';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
 
 export function completeTask(
-  pastEvents: TaskWasCompleted[],
+  pastEvents: LearningMaterialsTasksDomainEvent[],
   { data: { learningMaterialsId, taskId } }: CompleteTask,
 ): TaskWasCompleted[] {
   const state = pastEvents
@@ -13,6 +14,9 @@ export function completeTask(
           case 'TaskWasCompleted': {
             return { completed: true };
           }
+          case 'TaskWasUncompleted': {
+            return { completed: false };
+          }
           default: {
             return acc;
           }
diff --git a/packages/api/src/module/write/learning-materials-tasks/domain/events.ts b/packages/api/src/module/write/learning-materials-tasks/domain/events.ts
new file mode 100644
index 00000000..30e33d52
--- /dev/null
+++ b/packages/api/src/module/write/learning-materials-tasks/domain/events.ts
@@ -0,0 +1,4 @@
+import { TaskWasCompleted } from '@/events/task-was-completed.domain-event';
+import { TaskWasUncompleted } from '@/events/task-was-uncompleted-event.domain-event';
+
+export type LearningMaterialsTasksDomainEvent = TaskWasCompleted | TaskWasUncompleted;
diff --git a/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.spec.ts b/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.spec.ts
new file mode 100644
index 00000000..6882769a
--- /dev/null
+++ b/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.spec.ts
@@ -0,0 +1,60 @@
+import { UncompleteTask } from '@/commands/uncomplete-task.domain-command';
+import { TaskWasCompleted } from '@/events/task-was-completed.domain-event';
+import { TaskWasUncompleted } from '@/events/task-was-uncompleted-event.domain-event';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
+import { uncompleteTask } from '@/write/learning-materials-tasks/domain/uncomplete-task';
+
+describe('uncomplete task', () => {
+  const command: UncompleteTask = {
+    type: 'UncompleteTask',
+    data: { learningMaterialsId: 'sbAPITNMsl2wW6j2cg1H2A', taskId: 'L9EXtwmBNBXgo_qh0uzbq' },
+  };
+
+  it('should uncomplete completed task', () => {
+    // Given
+    const pastEvents: TaskWasCompleted[] = [
+      {
+        type: 'TaskWasCompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: 'L9EXtwmBNBXgo_qh0uzbq' },
+      },
+    ];
+
+    // When
+    const events = uncompleteTask(pastEvents, command);
+
+    // Then
+    expect(events).toStrictEqual([
+      {
+        type: 'TaskWasUncompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ]);
+  });
+
+  it('should throw an error if try to uncomplete uncompleted task', () => {
+    // given
+    const pastEvents: TaskWasUncompleted[] = [
+      {
+        type: 'TaskWasUncompleted',
+        data: { learningMaterialsId: command.data.learningMaterialsId, taskId: command.data.taskId },
+      },
+    ];
+
+    // when
+    const events = () => uncompleteTask(pastEvents, command);
+
+    // then
+    expect(events).toThrowError('Can not uncomplete task that was not completed yet.');
+  });
+
+  it('should throw an error if try to uncomplete task that was neither completed nor uncompleted yet', () => {
+    // given
+    const pastEvents: LearningMaterialsTasksDomainEvent[] = [];
+
+    // when
+    const events = () => uncompleteTask(pastEvents, command);
+
+    // then
+    expect(events).toThrowError('Can not uncomplete task that was not completed yet.');
+  });
+});
diff --git a/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.ts b/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.ts
new file mode 100644
index 00000000..2ddd058a
--- /dev/null
+++ b/packages/api/src/module/write/learning-materials-tasks/domain/uncomplete-task.ts
@@ -0,0 +1,41 @@
+import { UncompleteTask } from '@/commands/uncomplete-task.domain-command';
+import { TaskWasUncompleted } from '@/events/task-was-uncompleted-event.domain-event';
+import { LearningMaterialsTasksDomainEvent } from '@/write/learning-materials-tasks/domain/events';
+
+export function uncompleteTask(
+  pastEvents: LearningMaterialsTasksDomainEvent[],
+  { data: { learningMaterialsId, taskId } }: UncompleteTask,
+): TaskWasUncompleted[] {
+  const state = pastEvents
+    .filter(({ data }) => data.taskId === taskId)
+    .reduce<{ completed: boolean }>(
+      (acc, event) => {
+        switch (event.type) {
+          case 'TaskWasCompleted': {
+            return { completed: true };
+          }
+          case 'TaskWasUncompleted': {
+            return { completed: false };
+          }
+          default: {
+            return acc;
+          }
+        }
+      },
+      { completed: false },
+    );
+
+  if (!state.completed) {
+    throw new Error('Can not uncomplete task that was not completed yet.');
+  }
+
+  const newEvent: TaskWasUncompleted = {
+    type: 'TaskWasUncompleted',
+    data: {
+      taskId,
+      learningMaterialsId,
+    },
+  };
+
+  return [newEvent];
+}
diff --git a/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.spec.ts b/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.spec.ts
index 72ba47df..d80d63ab 100644
--- a/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.spec.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.spec.ts
@@ -1,22 +1,41 @@
 import { AsyncReturnType } from 'type-fest';
 
+import { UncompleteTaskApplicationCommand } from '@/commands/uncomplete-task.application-command';
+import { TaskWasUncompleted } from '@/events/task-was-uncompleted-event.domain-event';
 import { CompleteTaskApplicationCommand } from '@/module/commands/complete-task.application-command';
 import { TaskWasCompleted } from '@/module/events/task-was-completed.domain-event';
 
 import { EventStreamName } from '../shared/application/event-stream-name.value-object';
 import { learningMaterialsTasksTestModule } from './learning-materials-tasks.test-module';
 
+enum CommandType {
+  COMPLETE_TASK = 'Complete Task',
+  UNCOMPLETE_TASK = 'Uncomplete Task',
+}
+
 describe('learning materials tasks', () => {
   let module: AsyncReturnType<typeof learningMaterialsTasksTestModule>;
-  const commandBuilder = (taskId = 'VmkxXnPG02CaUNV8Relzk', learningMaterialsId = 'ZpMpw2eh1llFCGKZJEN6r') => ({
-    class: CompleteTaskApplicationCommand,
-    type: 'CompleteTask',
+  const commandBuilder = (
+    type: string,
+    taskId = 'VmkxXnPG02CaUNV8Relzk',
+    learningMaterialsId = 'ZpMpw2eh1llFCGKZJEN6r',
+  ) => ({
+    class: type === CommandType.COMPLETE_TASK ? CompleteTaskApplicationCommand : UncompleteTaskApplicationCommand,
+    type,
     data: { taskId, learningMaterialsId },
   });
 
+  beforeEach(async () => {
+    module = await learningMaterialsTasksTestModule();
+  });
+
+  afterEach(async () => {
+    await module.close();
+  });
+
   it('should change state of the task to complete', async () => {
     // Given
-    const command = commandBuilder();
+    const command = commandBuilder(CommandType.COMPLETE_TASK);
 
     // When
     await module.executeCommand(() => command);
@@ -34,7 +53,7 @@ describe('learning materials tasks', () => {
 
   it('should not change task state if task is already completed', async () => {
     // Given
-    const command = commandBuilder();
+    const command = commandBuilder(CommandType.COMPLETE_TASK);
 
     // When
     await module.executeCommand(() => command);
@@ -43,11 +62,34 @@ describe('learning materials tasks', () => {
     await expect(() => module.executeCommand(() => command)).rejects.toThrow();
   });
 
-  beforeEach(async () => {
-    module = await learningMaterialsTasksTestModule();
+  it('should change state of the task to uncomplete when task was completed already', async () => {
+    // Given
+    const completeCommand = commandBuilder(CommandType.COMPLETE_TASK);
+    const uncompleteCommand = commandBuilder(CommandType.UNCOMPLETE_TASK);
+
+    await module.executeCommand(() => completeCommand);
+
+    // When
+    await module.executeCommand(() => uncompleteCommand);
+
+    // Then
+    module.expectEventPublishedLastly<TaskWasUncompleted>({
+      type: 'TaskWasUncompleted',
+      data: {
+        learningMaterialsId: uncompleteCommand.data.learningMaterialsId,
+        taskId: uncompleteCommand.data.taskId,
+      },
+      streamName: EventStreamName.from('LearningMaterialsTasks', uncompleteCommand.data.learningMaterialsId),
+    });
   });
 
-  afterEach(async () => {
-    await module.close();
+  it('should not change state of the task to uncomplete if task was not completed before', async () => {
+    // Given
+    const uncompleteCommand = commandBuilder(CommandType.UNCOMPLETE_TASK);
+
+    // When&Then
+    await expect(() => module.executeCommand(() => uncompleteCommand)).rejects.toThrow(
+      'Can not uncomplete task that was not completed yet.',
+    );
   });
 });
diff --git a/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.ts b/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.ts
index acdd9c64..f071a7c0 100644
--- a/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/learning-materials-tasks.write-module.ts
@@ -1,12 +1,14 @@
 import { Module } from '@nestjs/common';
 
+import { UncompleteTaskCommandHandler } from '@/write/learning-materials-tasks/application/uncomplete-task.command-handler';
+
 import { SharedModule } from '../shared/shared.module';
 import { CompleteTaskCommandHandler } from './application/complete-task.command-handler';
 import { LearningMaterialsTaskRestController } from './presentation/rest/process-st-events.rest-controller';
 
 @Module({
   imports: [SharedModule],
-  providers: [CompleteTaskCommandHandler],
+  providers: [CompleteTaskCommandHandler, UncompleteTaskCommandHandler],
   controllers: [LearningMaterialsTaskRestController],
 })
 export class LearningMaterialsTasksModule {}
diff --git a/packages/api/src/module/write/learning-materials-tasks/presentation/rest/process-st-events.rest-controller.ts b/packages/api/src/module/write/learning-materials-tasks/presentation/rest/process-st-events.rest-controller.ts
index 49a44dc1..ca9dbfb1 100644
--- a/packages/api/src/module/write/learning-materials-tasks/presentation/rest/process-st-events.rest-controller.ts
+++ b/packages/api/src/module/write/learning-materials-tasks/presentation/rest/process-st-events.rest-controller.ts
@@ -1,6 +1,7 @@
 import { Body, Controller, HttpCode, Post } from '@nestjs/common';
 import { CommandBus } from '@nestjs/cqrs';
 
+import { UncompleteTaskApplicationCommand } from '@/commands/uncomplete-task.application-command';
 import { CompleteTaskApplicationCommand } from '@/module/commands/complete-task.application-command';
 import { ApplicationCommandFactory } from '@/write/shared/application/application-command.factory';
 
@@ -24,5 +25,13 @@ export class LearningMaterialsTaskRestController {
 
       await this.commandBus.execute(command);
     }
+
+    const command = this.commandFactory.applicationCommand(() => ({
+      class: UncompleteTaskApplicationCommand,
+      type: 'UncompleteTask',
+      data: { learningMaterialsId, taskId },
+    }));
+
+    await this.commandBus.execute(command);
   }
 }