diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44aef588c..eca100306 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -199,6 +199,7 @@ Docs: https://docs.openclaw.ai
 - Telegram/Discord media upload caps: make outbound uploads honor channel `mediaMaxMb` config, raise Telegram's default media cap to 100MB, and remove MIME fallback limits that kept some Telegram uploads at 16MB. Thanks @vincentkoc.
 - Skills/nano-banana-pro resolution override: respect explicit `--resolution` values during image editing and only auto-detect output size from input images when the flag is omitted. (#36880) Thanks @shuofengzhang and @vincentkoc.
 - Skills/openai-image-gen CLI validation: validate `--background` and `--style` inputs early, normalize supported values, and warn when those flags are ignored for incompatible models. (#36762) Thanks @shuofengzhang and @vincentkoc.
+- WhatsApp media upload caps: make outbound media sends and auto-replies honor `channels.whatsapp.mediaMaxMb` with per-account overrides so inbound and outbound limits use the same channel config. Thanks @vincentkoc.
 
 ## 2026.3.2
 
diff --git a/docs/channels/whatsapp.md b/docs/channels/whatsapp.md
index d92dfda9c..cad9fe77e 100644
--- a/docs/channels/whatsapp.md
+++ b/docs/channels/whatsapp.md
@@ -308,7 +308,8 @@ When the linked self number is also present in `allowFrom`, WhatsApp self-chat s
 
   <Accordion title="Media size limits and fallback behavior">
     - inbound media save cap: `channels.whatsapp.mediaMaxMb` (default `50`)
-    - outbound media cap for auto-replies: `agents.defaults.mediaMaxMb` (default `5MB`)
+    - outbound media send cap: `channels.whatsapp.mediaMaxMb` (default `50`)
+    - per-account overrides use `channels.whatsapp.accounts.<accountId>.mediaMaxMb`
     - images are auto-optimized (resize/quality sweep) to fit limits
     - on media send failure, first-item fallback sends text warning instead of dropping the response silently
   </Accordion>
diff --git a/src/web/accounts.ts b/src/web/accounts.ts
index 52fb5caab..3370d4c9d 100644
--- a/src/web/accounts.ts
+++ b/src/web/accounts.ts
@@ -31,6 +31,8 @@ export type ResolvedWhatsAppAccount = {
   debounceMs?: number;
 };
 
+export const DEFAULT_WHATSAPP_MEDIA_MAX_MB = 50;
+
 const { listConfiguredAccountIds, listAccountIds, resolveDefaultAccountId } =
   createAccountListHelpers("whatsapp");
 export const listWhatsAppAccountIds = listAccountIds;
@@ -147,6 +149,16 @@ export function resolveWhatsAppAccount(params: {
   };
 }
 
+export function resolveWhatsAppMediaMaxBytes(
+  account: Pick<ResolvedWhatsAppAccount, "mediaMaxMb">,
+): number {
+  const mediaMaxMb =
+    typeof account.mediaMaxMb === "number" && account.mediaMaxMb > 0
+      ? account.mediaMaxMb
+      : DEFAULT_WHATSAPP_MEDIA_MAX_MB;
+  return mediaMaxMb * 1024 * 1024;
+}
+
 export function listEnabledWhatsAppAccounts(cfg: OpenClawConfig): ResolvedWhatsAppAccount[] {
   return listWhatsAppAccountIds(cfg)
     .map((accountId) => resolveWhatsAppAccount({ cfg, accountId }))
diff --git a/src/web/auto-reply.web-auto-reply.compresses-common-formats-jpeg-cap.test.ts b/src/web/auto-reply.web-auto-reply.compresses-common-formats-jpeg-cap.test.ts
index 9d74ece0e..7d9e5150d 100644
--- a/src/web/auto-reply.web-auto-reply.compresses-common-formats-jpeg-cap.test.ts
+++ b/src/web/auto-reply.web-auto-reply.compresses-common-formats-jpeg-cap.test.ts
@@ -73,7 +73,14 @@ describe("web auto-reply", () => {
   }
 
   async function withMediaCap<T>(mediaMaxMb: number, run: () => Promise<T>): Promise<T> {
-    setLoadConfigMock(() => ({ agents: { defaults: { mediaMaxMb } } }));
+    setLoadConfigMock(() => ({
+      channels: {
+        whatsapp: {
+          allowFrom: ["*"],
+          mediaMaxMb,
+        },
+      },
+    }));
     try {
       return await run();
     } finally {
@@ -215,7 +222,7 @@ describe("web auto-reply", () => {
     });
   });
 
-  it("honors mediaMaxMb from config", async () => {
+  it("honors channels.whatsapp.mediaMaxMb for outbound auto-replies", async () => {
     const bigPng = await sharp({
       create: {
         width: 256,
@@ -235,6 +242,53 @@ describe("web auto-reply", () => {
       mediaMaxMb: SMALL_MEDIA_CAP_MB,
     });
   });
+
+  it("prefers per-account WhatsApp media caps for outbound auto-replies", async () => {
+    const bigPng = await sharp({
+      create: {
+        width: 256,
+        height: 256,
+        channels: 3,
+        background: { r: 255, g: 0, b: 0 },
+      },
+    })
+      .png({ compressionLevel: 0 })
+      .toBuffer();
+    expect(bigPng.length).toBeGreaterThan(SMALL_MEDIA_CAP_BYTES);
+
+    setLoadConfigMock(() => ({
+      channels: {
+        whatsapp: {
+          allowFrom: ["*"],
+          mediaMaxMb: 1,
+          accounts: {
+            work: {
+              mediaMaxMb: SMALL_MEDIA_CAP_MB,
+            },
+          },
+        },
+      },
+    }));
+
+    try {
+      const sendMedia = vi.fn();
+      const { reply, dispatch } = await setupSingleInboundMessage({
+        resolverValue: { text: "hi", mediaUrl: "https://example.com/account-big.png" },
+        sendMedia,
+      });
+      const fetchMock = mockFetchMediaBuffer(bigPng, "image/png");
+
+      await dispatch("msg-account-cap", { accountId: "work" });
+
+      const payload = getSingleImagePayload(sendMedia);
+      expect(payload.image.length).toBeLessThanOrEqual(SMALL_MEDIA_CAP_BYTES);
+      expect(payload.mimetype).toBe("image/jpeg");
+      expect(reply).not.toHaveBeenCalled();
+      fetchMock.mockRestore();
+    } finally {
+      resetLoadConfigMock();
+    }
+  });
   it("falls back to text when media is unsupported", async () => {
     const sendMedia = vi.fn();
     const { reply, dispatch } = await setupSingleInboundMessage({
diff --git a/src/web/auto-reply/monitor.ts b/src/web/auto-reply/monitor.ts
index b7e2bb268..66b9c0fd9 100644
--- a/src/web/auto-reply/monitor.ts
+++ b/src/web/auto-reply/monitor.ts
@@ -12,7 +12,7 @@ import { registerUnhandledRejectionHandler } from "../../infra/unhandled-rejecti
 import { getChildLogger } from "../../logging.js";
 import { resolveAgentRoute } from "../../routing/resolve-route.js";
 import { defaultRuntime, type RuntimeEnv } from "../../runtime.js";
-import { resolveWhatsAppAccount } from "../accounts.js";
+import { resolveWhatsAppAccount, resolveWhatsAppMediaMaxBytes } from "../accounts.js";
 import { setActiveWebListener } from "../active-listener.js";
 import { monitorWebInbox } from "../inbound.js";
 import {
@@ -23,7 +23,6 @@ import {
   sleepWithAbort,
 } from "../reconnect.js";
 import { formatError, getWebAuthAgeMs, readWebSelfId } from "../session.js";
-import { DEFAULT_WEB_MEDIA_BYTES } from "./constants.js";
 import { whatsappHeartbeatLog, whatsappLog } from "./loggers.js";
 import { buildMentionConfig } from "./mentions.js";
 import { createEchoTracker } from "./monitor/echo.js";
@@ -93,11 +92,7 @@ export async function monitorWebChannel(
     },
   } satisfies ReturnType<typeof loadConfig>;
 
-  const configuredMaxMb = cfg.agents?.defaults?.mediaMaxMb;
-  const maxMediaBytes =
-    typeof configuredMaxMb === "number" && configuredMaxMb > 0
-      ? configuredMaxMb * 1024 * 1024
-      : DEFAULT_WEB_MEDIA_BYTES;
+  const maxMediaBytes = resolveWhatsAppMediaMaxBytes(account);
   const heartbeatSeconds = resolveHeartbeatSeconds(cfg, tuning.heartbeatSeconds);
   const reconnectPolicy = resolveReconnectPolicy(cfg, tuning.reconnect);
   const baseMentionConfig = buildMentionConfig(cfg);
diff --git a/src/web/outbound.test.ts b/src/web/outbound.test.ts
index e60d15158..e494392d7 100644
--- a/src/web/outbound.test.ts
+++ b/src/web/outbound.test.ts
@@ -3,6 +3,7 @@ import fsSync from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import type { OpenClawConfig } from "../config/config.js";
 import { resetLogger, setLoggerOverride } from "../logging.js";
 import { redactIdentifier } from "../logging/redact-identifier.js";
 import { setActiveWebListener } from "./active-listener.js";
@@ -34,6 +35,7 @@ describe("web outbound", () => {
     resetLogger();
     setLoggerOverride(null);
     setActiveWebListener(null);
+    setActiveWebListener("work", null);
   });
 
   it("sends message via active listener", async () => {
@@ -140,6 +142,46 @@ describe("web outbound", () => {
     });
   });
 
+  it("uses account-aware WhatsApp media caps for outbound uploads", async () => {
+    setActiveWebListener("work", {
+      sendComposingTo,
+      sendMessage,
+      sendPoll,
+      sendReaction,
+    });
+    loadWebMediaMock.mockResolvedValueOnce({
+      buffer: Buffer.from("img"),
+      contentType: "image/jpeg",
+      kind: "image",
+    });
+
+    const cfg = {
+      channels: {
+        whatsapp: {
+          mediaMaxMb: 25,
+          accounts: {
+            work: {
+              mediaMaxMb: 100,
+            },
+          },
+        },
+      },
+    } as OpenClawConfig;
+
+    await sendMessageWhatsApp("+1555", "pic", {
+      verbose: false,
+      accountId: "work",
+      cfg,
+      mediaUrl: "/tmp/pic.jpg",
+      mediaLocalRoots: ["/tmp/workspace"],
+    });
+
+    expect(loadWebMediaMock).toHaveBeenCalledWith("/tmp/pic.jpg", {
+      maxBytes: 100 * 1024 * 1024,
+      localRoots: ["/tmp/workspace"],
+    });
+  });
+
   it("sends polls via active listener", async () => {
     const result = await sendPollWhatsApp(
       "+1555",
diff --git a/src/web/outbound.ts b/src/web/outbound.ts
index 95cc84b1f..43136c6f7 100644
--- a/src/web/outbound.ts
+++ b/src/web/outbound.ts
@@ -8,6 +8,7 @@ import { convertMarkdownTables } from "../markdown/tables.js";
 import { markdownToWhatsApp } from "../markdown/whatsapp.js";
 import { normalizePollInput, type PollInput } from "../polls.js";
 import { toWhatsappJid } from "../utils.js";
+import { resolveWhatsAppAccount, resolveWhatsAppMediaMaxBytes } from "./accounts.js";
 import { type ActiveWebSendOptions, requireActiveWebListener } from "./active-listener.js";
 import { loadWebMedia } from "./media.js";
 
@@ -32,6 +33,10 @@ export async function sendMessageWhatsApp(
     options.accountId,
   );
   const cfg = options.cfg ?? loadConfig();
+  const account = resolveWhatsAppAccount({
+    cfg,
+    accountId: resolvedAccountId ?? options.accountId,
+  });
   const tableMode = resolveMarkdownTableMode({
     cfg,
     channel: "whatsapp",
@@ -53,6 +58,7 @@ export async function sendMessageWhatsApp(
     let documentFileName: string | undefined;
     if (options.mediaUrl) {
       const media = await loadWebMedia(options.mediaUrl, {
+        maxBytes: resolveWhatsAppMediaMaxBytes(account),
         localRoots: options.mediaLocalRoots,
       });
       const caption = text || undefined;