diff --git a/src/agents/tools/slack-actions.e2e.test.ts b/src/agents/tools/slack-actions.e2e.test.ts
index fbba80d8f64..a123365cc9f 100644
--- a/src/agents/tools/slack-actions.e2e.test.ts
+++ b/src/agents/tools/slack-actions.e2e.test.ts
@@ -221,6 +221,21 @@ describe("handleSlackAction", () => {
     ).rejects.toThrow(/requires content, blocks, or mediaUrl/i);
   });
 
+  it("rejects blocks combined with mediaUrl", async () => {
+    const cfg = { channels: { slack: { botToken: "tok" } } } as OpenClawConfig;
+    await expect(
+      handleSlackAction(
+        {
+          action: "sendMessage",
+          to: "channel:C123",
+          blocks: [{ type: "divider" }],
+          mediaUrl: "https://example.com/image.png",
+        },
+        cfg,
+      ),
+    ).rejects.toThrow(/does not support blocks with mediaUrl/i);
+  });
+
   it("passes blocks JSON to editSlackMessage with empty content", async () => {
     const cfg = { channels: { slack: { botToken: "tok" } } } as OpenClawConfig;
     editSlackMessage.mockClear();
diff --git a/src/agents/tools/slack-actions.ts b/src/agents/tools/slack-actions.ts
index eff7ba45ec8..1350cb62561 100644
--- a/src/agents/tools/slack-actions.ts
+++ b/src/agents/tools/slack-actions.ts
@@ -185,6 +185,9 @@ export async function handleSlackAction(
         if (!content && !mediaUrl && !blocks) {
           throw new Error("Slack sendMessage requires content, blocks, or mediaUrl.");
         }
+        if (mediaUrl && blocks) {
+          throw new Error("Slack sendMessage does not support blocks with mediaUrl.");
+        }
         const threadTs = resolveThreadTsFromContext(
           readStringParam(params, "threadTs"),
           to,
diff --git a/src/channels/plugins/actions/actions.test.ts b/src/channels/plugins/actions/actions.test.ts
index 86cd5b12365..563c38ce898 100644
--- a/src/channels/plugins/actions/actions.test.ts
+++ b/src/channels/plugins/actions/actions.test.ts
@@ -613,6 +613,26 @@ describe("slack actions adapter", () => {
     expect(handleSlackAction).not.toHaveBeenCalled();
   });
 
+  it("rejects send when both blocks and media are provided", async () => {
+    const cfg = { channels: { slack: { botToken: "tok" } } } as OpenClawConfig;
+    const actions = createSlackActions("slack");
+
+    await expect(
+      actions.handleAction?.({
+        channel: "slack",
+        action: "send",
+        cfg,
+        params: {
+          to: "channel:C1",
+          message: "",
+          media: "https://example.com/image.png",
+          blocks: JSON.stringify([{ type: "divider" }]),
+        },
+      }),
+    ).rejects.toThrow(/does not support blocks with media/i);
+    expect(handleSlackAction).not.toHaveBeenCalled();
+  });
+
   it("forwards blocks JSON for edit", async () => {
     const cfg = { channels: { slack: { botToken: "tok" } } } as OpenClawConfig;
     const actions = createSlackActions("slack");
diff --git a/src/plugin-sdk/slack-message-actions.ts b/src/plugin-sdk/slack-message-actions.ts
index 8cff504708f..d5a757b80dc 100644
--- a/src/plugin-sdk/slack-message-actions.ts
+++ b/src/plugin-sdk/slack-message-actions.ts
@@ -41,6 +41,9 @@ export async function handleSlackMessageAction(params: {
     if (!content && !mediaUrl && !blocks) {
       throw new Error("Slack send requires message, blocks, or media.");
     }
+    if (mediaUrl && blocks) {
+      throw new Error("Slack send does not support blocks with media.");
+    }
     const threadId = readStringParam(actionParams, "threadId");
     const replyTo = readStringParam(actionParams, "replyTo");
     return await invoke(