diff --git a/docs/channels/mattermost.md b/docs/channels/mattermost.md
index 3517736f620..f9417109a77 100644
--- a/docs/channels/mattermost.md
+++ b/docs/channels/mattermost.md
@@ -224,6 +224,8 @@ Config:
 - `channels.mattermost.interactions.callbackBaseUrl`: optional external base URL for button
   callbacks (for example `https://gateway.example.com`). Use this when Mattermost cannot
   reach the gateway at its bind host directly.
+- In multi-account setups, you can also set the same field under
+  `channels.mattermost.accounts.<id>.interactions.callbackBaseUrl`.
 - If `interactions.callbackBaseUrl` is omitted, OpenClaw derives the callback URL from
   `gateway.customBindHost` + `gateway.port`, then falls back to `http://localhost:<port>`.
 - Reachability rule: the button callback URL must be reachable from the Mattermost server.
diff --git a/extensions/mattermost/src/channel.ts b/extensions/mattermost/src/channel.ts
index 5897c11277a..00e4c69e0f7 100644
--- a/extensions/mattermost/src/channel.ts
+++ b/extensions/mattermost/src/channel.ts
@@ -165,7 +165,10 @@ const mattermostMessageActions: ChannelMessageActionAdapter = {
     if (params.buttons && Array.isArray(params.buttons)) {
       const account = resolveMattermostAccount({ cfg, accountId: resolvedAccountId });
       if (account.botToken) setInteractionSecret(account.accountId, account.botToken);
-      const callbackUrl = resolveInteractionCallbackUrl(account.accountId, cfg);
+      const callbackUrl = resolveInteractionCallbackUrl(account.accountId, {
+        gateway: cfg.gateway,
+        interactions: account.config.interactions,
+      });
 
       // Flatten 2D array (rows of buttons) to 1D — core schema sends Array<Array<Button>>
       // but Mattermost doesn't have row layout, so we flatten all rows into a single list.
diff --git a/extensions/mattermost/src/mattermost/interactions.test.ts b/extensions/mattermost/src/mattermost/interactions.test.ts
index 032e3430c6a..2ad979b1a49 100644
--- a/extensions/mattermost/src/mattermost/interactions.test.ts
+++ b/extensions/mattermost/src/mattermost/interactions.test.ts
@@ -1,6 +1,7 @@
 import { type IncomingMessage, type ServerResponse } from "node:http";
 import { describe, expect, it, beforeEach, afterEach } from "vitest";
 import { setMattermostRuntime } from "../runtime.js";
+import { resolveMattermostAccount } from "./accounts.js";
 import type { MattermostClient } from "./client.js";
 import {
   buildButtonAttachments,
@@ -169,6 +170,35 @@ describe("resolveInteractionCallbackUrl", () => {
     expect(url).toBe("https://gateway.example.com/root/mattermost/interactions/acct");
   });
 
+  it("uses merged per-account interactions.callbackBaseUrl", () => {
+    const cfg = {
+      gateway: { port: 9999 },
+      channels: {
+        mattermost: {
+          accounts: {
+            acct: {
+              botToken: "bot-token",
+              baseUrl: "https://chat.example.com",
+              interactions: {
+                callbackBaseUrl: "https://gateway.example.com/root",
+              },
+            },
+          },
+        },
+      },
+    };
+    const account = resolveMattermostAccount({
+      cfg,
+      accountId: "acct",
+      allowUnresolvedSecretRef: true,
+    });
+    const url = resolveInteractionCallbackUrl(account.accountId, {
+      gateway: cfg.gateway,
+      interactions: account.config.interactions,
+    });
+    expect(url).toBe("https://gateway.example.com/root/mattermost/interactions/acct");
+  });
+
   it("falls back to gateway.customBindHost when configured", () => {
     const url = resolveInteractionCallbackUrl("default", {
       gateway: { port: 9999, customBindHost: "gateway.internal" },
diff --git a/extensions/mattermost/src/mattermost/interactions.ts b/extensions/mattermost/src/mattermost/interactions.ts
index 79c87197352..6685e194c7d 100644
--- a/extensions/mattermost/src/mattermost/interactions.ts
+++ b/extensions/mattermost/src/mattermost/interactions.ts
@@ -44,7 +44,11 @@ export function getInteractionCallbackUrl(accountId: string): string | undefined
   return callbackUrls.get(accountId);
 }
 
-type InteractionCallbackConfig = Pick<OpenClawConfig, "gateway" | "channels">;
+type InteractionCallbackConfig = Pick<OpenClawConfig, "gateway" | "channels"> & {
+  interactions?: {
+    callbackBaseUrl?: string;
+  };
+};
 
 export function resolveInteractionCallbackPath(accountId: string): string {
   return `/mattermost/interactions/${accountId}`;
@@ -75,7 +79,11 @@ export function resolveInteractionCallbackUrl(
     return cached;
   }
   const path = resolveInteractionCallbackPath(accountId);
-  const callbackBaseUrl = cfg?.channels?.mattermost?.interactions?.callbackBaseUrl?.trim();
+  // Prefer merged per-account config when available, but keep the top-level path for
+  // callers/tests that still pass the root Mattermost config shape directly.
+  const callbackBaseUrl =
+    cfg?.interactions?.callbackBaseUrl?.trim() ??
+    cfg?.channels?.mattermost?.interactions?.callbackBaseUrl?.trim();
   if (callbackBaseUrl) {
     return `${normalizeCallbackBaseUrl(callbackBaseUrl)}${path}`;
   }
diff --git a/extensions/mattermost/src/mattermost/monitor.ts b/extensions/mattermost/src/mattermost/monitor.ts
index 92e8bf71f51..8546f0a0983 100644
--- a/extensions/mattermost/src/mattermost/monitor.ts
+++ b/extensions/mattermost/src/mattermost/monitor.ts
@@ -456,7 +456,10 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
   // Register HTTP callback endpoint for interactive button clicks.
   // Mattermost POSTs to this URL when a user clicks a button action.
   const interactionPath = resolveInteractionCallbackPath(account.accountId);
-  const callbackUrl = resolveInteractionCallbackUrl(account.accountId, cfg);
+  const callbackUrl = resolveInteractionCallbackUrl(account.accountId, {
+    gateway: cfg.gateway,
+    interactions: account.config.interactions,
+  });
   setInteractionCallbackUrl(account.accountId, callbackUrl);
 
   try {