diff --git a/example_config.json b/example_config.json
index 2bb760e..c3073e0 100644
--- a/example_config.json
+++ b/example_config.json
@@ -62,6 +62,52 @@
                     "unique": false
                 }
             ]
+        },
+        {
+            "name": "posts",
+            "fields": [
+                {
+                    "name": "id",
+                    "type": "integer",
+                    "primaryKey": true
+                },
+                {
+                    "name": "title",
+                    "type": "string",
+                    "nullable": false
+                },
+                {
+                    "name": "body",
+                    "type": "text",
+                    "nullable": true
+                },
+                {
+                    "name": "user_id",
+                    "type": "integer",
+                    "nullable": false
+                },
+                {
+                    "name": "created_at",
+                    "type": "datetime"
+                }
+            ],
+            "indexes": [
+                {
+                    "name": "posts_user_id_idx",
+                    "columns": ["user_id"],
+                    "unique": false
+                }
+            ],
+            "foreignKeys": [
+                {
+                    "name": "fk_posts_user_id",
+                    "columns": ["user_id"],
+                    "referenceTable": "users",
+                    "referenceColumns": ["id"],
+                    "onDelete": "CASCADE",
+                    "onUpdate": "CASCADE"
+                }
+            ]
         }
     ]
 }
\ No newline at end of file
diff --git a/src/database/fk-creator.ts b/src/database/fk-creator.ts
new file mode 100644
index 0000000..8909f66
--- /dev/null
+++ b/src/database/fk-creator.ts
@@ -0,0 +1,74 @@
+import { DatabaseQuery, ModelConfig, DBEngine } from '../types';
+
+const VALID_IDENTIFIER = /^[a-zA-Z_][a-zA-Z0-9_]*$/;
+
+function validateIdentifier(value: string, label: string) {
+  if (!VALID_IDENTIFIER.test(value)) {
+    throw new Error(`Invalid ${label}: ${value}`);
+  }
+}
+
+export async function createForeignKeys(
+  db: DatabaseQuery,
+  models: ModelConfig[],
+  engine: DBEngine,
+  logger: { info: (msg: string) => void; warn: (msg: string) => void }
+) {
+  for (const model of models) {
+    if (!model.foreignKeys || model.foreignKeys.length === 0) continue;
+
+    for (const fk of model.foreignKeys) {
+      validateIdentifier(fk.name, 'foreign key name');
+      validateIdentifier(model.name, 'table name');
+      validateIdentifier(fk.referenceTable, 'reference table name');
+      for (const col of fk.columns) {
+        validateIdentifier(col, `column name in FK "${fk.name}"`);
+      }
+      for (const col of fk.referenceColumns) {
+        validateIdentifier(col, `reference column name in FK "${fk.name}"`);
+      }
+
+      // Check if constraint already exists
+      let fkExists = false;
+      if (engine === 'pg') {
+        const res = await db.query<string, { exists: boolean }>(
+          "SELECT EXISTS (SELECT FROM information_schema.table_constraints WHERE constraint_name = $1 AND constraint_type = 'FOREIGN KEY')",
+          [fk.name]
+        );
+        fkExists = res[0].exists;
+      } else {
+        // SQLite doesn't support ALTER TABLE ADD CONSTRAINT for FKs.
+        // FKs must be defined at table creation time in SQLite.
+        logger.warn(
+          `SQLite does not support adding foreign keys via ALTER TABLE. FK "${fk.name}" on "${model.name}" skipped.`
+        );
+        continue;
+      }
+
+      if (fkExists) {
+        logger.info(`Foreign key "${fk.name}" on table "${model.name}" already exists, skipping.`);
+        continue;
+      }
+
+      const columnList = fk.columns.map((c) => `"${c}"`).join(', ');
+      const refColumnList = fk.referenceColumns.map((c) => `"${c}"`).join(', ');
+
+      let sql = `ALTER TABLE "${model.name}" ADD CONSTRAINT "${fk.name}" FOREIGN KEY (${columnList}) REFERENCES "${fk.referenceTable}" (${refColumnList})`;
+
+      if (fk.onDelete) {
+        sql += ` ON DELETE ${fk.onDelete}`;
+      }
+      if (fk.onUpdate) {
+        sql += ` ON UPDATE ${fk.onUpdate}`;
+      }
+
+      sql += ';';
+
+      logger.info(
+        `Creating foreign key "${fk.name}" on "${model.name}" referencing "${fk.referenceTable}" (${fk.referenceColumns.join(', ')})...`
+      );
+      await db.query(sql);
+      logger.info(`Foreign key "${fk.name}" created successfully.`);
+    }
+  }
+}
diff --git a/src/server.ts b/src/server.ts
index b179a31..09cc0ff 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -7,6 +7,7 @@ import { AppConfig, Mode } from './types';
 import dbPlugin from './plugin/database';
 import { createTables } from './database/table-creator';
 import { createIndexes } from './database/index-creator';
+import { createForeignKeys } from './database/fk-creator';
 
 async function registerSwagger(swaggerConfig: AppConfig['swagger'], app: FastifyInstance) {
   if (swaggerConfig.enabled) {
@@ -79,10 +80,11 @@ export async function startServer(config: AppConfig, port: number, mode: Mode) {
     connection: config.database.connection,
   });
 
-  // Auto-generate tables and indexes if models are provided
+  // Auto-generate tables, indexes, and foreign keys if models are provided
   if (config.models && config.models.length > 0) {
     await createTables(app.db, config.models, config.database.engine, app.log);
     await createIndexes(app.db, config.models, config.database.engine, app.log);
+    await createForeignKeys(app.db, config.models, config.database.engine, app.log);
   }
 
   // register swagger
diff --git a/src/types/index.ts b/src/types/index.ts
index e45ec08..440b953 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -2,6 +2,7 @@ export type Mode = 'dev' | 'prod';
 export type HTTPMethod = 'GET' | 'POST' | 'PUT' | 'DELETE';
 export type DBEngine = 'sqlite' | 'pg';
 export type DataType = 'integer' | 'string' | 'boolean' | 'text' | 'datetime';
+export type ForeignKeyAction = 'CASCADE' | 'SET NULL' | 'SET DEFAULT' | 'RESTRICT' | 'NO ACTION';
 
 export interface CLIOptions {
   config: string;
@@ -62,10 +63,20 @@ export interface ModelIndex {
   unique?: boolean;
 }
 
+export interface ModelForeignKey {
+  name: string;
+  columns: string[];
+  referenceTable: string;
+  referenceColumns: string[];
+  onDelete?: ForeignKeyAction;
+  onUpdate?: ForeignKeyAction;
+}
+
 export interface ModelConfig {
   name: string;
   fields: ModelField[];
   indexes?: ModelIndex[];
+  foreignKeys?: ModelForeignKey[];
 }
 
 export interface AppConfig {