diff --git a/src/lib/__tests__/sendMessage.js b/src/lib/__tests__/sendMessage.js
index 0e505e56..6007702b 100644
--- a/src/lib/__tests__/sendMessage.js
+++ b/src/lib/__tests__/sendMessage.js
@@ -6,7 +6,7 @@ import rollbar from 'src/lib/rollbar';
 import sendMessage from '../sendMessage';
 
 beforeEach(() => {
-  fetch.mockClear();
+  fetch.mockReset();
   rollbar.error.mockClear();
 });
 
@@ -29,8 +29,12 @@ it('send message using LINE Notify', () => {
   `);
 });
 
-it('send message using multicast api', () => {
-  sendMessage.multicast(
+it('send message using multicast api', async () => {
+  fetch.mockImplementation(() =>
+    Promise.resolve({ json: () => Promise.resolve({ status: 200 }) })
+  );
+
+  await sendMessage.multicast(
     ['userId1', 'userId2', 'userId3'],
     [{ type: 'text', text: 'message' }]
   );
@@ -49,6 +53,30 @@ it('send message using multicast api', () => {
       ],
     ]
   `);
+
+  // Test batching
+  fetch.mockClear();
+  await sendMessage.multicast(
+    Array.from(Array(501)).map((_, id) => `user${id}`),
+    [{ type: 'text', text: 'message' }]
+  );
+
+  expect(fetch.mock.calls).toHaveLength(2);
+
+  // The snapshot of the "second batch", which should only contain user500
+  expect(fetch.mock.calls[1]).toMatchInlineSnapshot(`
+    Array [
+      "https://api.line.me/v2/bot/message/multicast",
+      Object {
+        "body": "{\\"to\\":[\\"user500\\"],\\"messages\\":[{\\"type\\":\\"text\\",\\"text\\":\\"message\\"}]}",
+        "headers": Object {
+          "Authorization": "Bearer ",
+          "Content-Type": "application/json",
+        },
+        "method": "POST",
+      },
+    ]
+  `);
 });
 
 it('send message using push api', () => {
diff --git a/src/lib/sendMessage.js b/src/lib/sendMessage.js
index b2a4a9bc..ce7b60be 100644
--- a/src/lib/sendMessage.js
+++ b/src/lib/sendMessage.js
@@ -10,16 +10,40 @@ const notify = async (token, message) => {
   lineNotify(token, { message: message });
 };
 
+/**
+ * Split large array into list of batches, with max size being batchSize for each batch
+ * @param {Array<*>} array
+ * @param {number} batchSize
+ * @returns {Array<Array<*>>}
+ */
+function batch(array, batchSize) {
+  return array.reduce(
+    (batches, item) => {
+      if (batches[batches.length - 1].length >= batchSize) {
+        batches.push([]);
+      }
+      batches[batches.length - 1].push(item);
+      return batches;
+    },
+    [[]]
+  );
+}
+
 /**
  * https://developers.line.biz/en/reference/messaging-api/#send-multicast-message
  * @param {string[]} userIds
  * @param {object[]} messages - Array of line message objects, max size:5
  */
 const multicast = async (userIds, messages) => {
-  lineClient.post('/message/multicast', {
-    to: userIds,
-    messages: messages,
-  });
+  for (const userIdBatch of batch(
+    userIds,
+    500 /* Multicast can send to 500 ppl in max each time */
+  )) {
+    await lineClient.post('/message/multicast', {
+      to: userIdBatch,
+      messages: messages,
+    });
+  }
 };
 
 /**
@@ -27,12 +51,11 @@ const multicast = async (userIds, messages) => {
  * @param {string} userId
  * @param {object[]} messages - Array of line message objects, max size:5
  */
-const push = async (userId, messages) => {
+const push = (userId, messages) =>
   lineClient.post('/message/push', {
     to: userId,
     messages: messages,
   });
-};
 
 export default {
   notify,