diff --git a/extensions/slack/src/monitor/message-handler/prepare.test.ts b/extensions/slack/src/monitor/message-handler/prepare.test.ts
index 0ea12b699bab..48c7296a089a 100644
--- a/extensions/slack/src/monitor/message-handler/prepare.test.ts
+++ b/extensions/slack/src/monitor/message-handler/prepare.test.ts
@@ -188,6 +188,14 @@ describe("slack prepareSlackMessage inbound contract", () => {
     expect(prepared.ctxPayload.BodyForAgent).toContain(body);
   });
 
+  it("keeps a whole code point when the inbound preview boundary crosses an emoji", async () => {
+    const prefix = "a".repeat(159);
+    const prepared = await prepareWithDefaultCtx(createSlackMessage({ text: `${prefix}😀tail` }));
+
+    assertPrepared(prepared);
+    expect(prepared.preview).toBe(prefix);
+  });
+
   it("logs inbound metadata without logging message content", async () => {
     const body = "confidential acquisition target: northstar; do not include this text in logs";
     shouldLogVerboseMock.mockReturnValue(true);
diff --git a/extensions/slack/src/monitor/message-handler/prepare.ts b/extensions/slack/src/monitor/message-handler/prepare.ts
index 08cf005b39f4..b3c17c6bf5ca 100644
--- a/extensions/slack/src/monitor/message-handler/prepare.ts
+++ b/extensions/slack/src/monitor/message-handler/prepare.ts
@@ -35,6 +35,7 @@ import {
   normalizeOptionalString,
 } from "openclaw/plugin-sdk/string-coerce-runtime";
 import { enqueueSystemEvent } from "openclaw/plugin-sdk/system-event-runtime";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import { resolveSlackReplyToMode } from "../../account-reply-mode.js";
 import type { ResolvedSlackAccount } from "../../accounts.js";
 import { reactSlackMessage } from "../../actions.js";
@@ -1210,7 +1211,7 @@ export async function prepareSlackMessage(params: {
 
   const roomLabel = channelName ? `#${channelName}` : `#${message.channel}`;
   const senderName = await resolveSenderName();
-  const preview = rawBody.replace(/\s+/g, " ").slice(0, 160);
+  const preview = truncateUtf16Safe(rawBody.replace(/\s+/g, " "), 160);
   const inboundLabel = isDirectMessage
     ? `Slack DM from ${senderName}`
     : `Slack message in ${roomLabel} from ${senderName}`;