diff --git a/agentscope-core/src/main/java/io/agentscope/core/message/ToolResultBlock.java b/agentscope-core/src/main/java/io/agentscope/core/message/ToolResultBlock.java
index 3f64596f2..80eb5751f 100644
--- a/agentscope-core/src/main/java/io/agentscope/core/message/ToolResultBlock.java
+++ b/agentscope-core/src/main/java/io/agentscope/core/message/ToolResultBlock.java
@@ -199,15 +199,19 @@ public static ToolResultBlock text(String text) {
     /**
      * Create an error result (for tool method return values).
      *
+     * <p>The result carries {@link ToolResultState#ERROR} so that failures are
+     * recognized by state, independent of the output text prefix.
+     *
      * @param errorMessage Error message
-     * @return ToolResultBlock with error output
+     * @return ToolResultBlock with error output and {@code state = ERROR}
      */
     public static ToolResultBlock error(String errorMessage) {
         return new ToolResultBlock(
                 null,
                 null,
                 List.of(TextBlock.builder().text("Error: " + errorMessage).build()),
-                null);
+                null,
+                ToolResultState.ERROR);
     }
 
     /**
diff --git a/agentscope-core/src/test/java/io/agentscope/core/tool/ToolExecutorTest.java b/agentscope-core/src/test/java/io/agentscope/core/tool/ToolExecutorTest.java
index b123c3ac9..9ef4cc9a3 100644
--- a/agentscope-core/src/test/java/io/agentscope/core/tool/ToolExecutorTest.java
+++ b/agentscope-core/src/test/java/io/agentscope/core/tool/ToolExecutorTest.java
@@ -22,6 +22,7 @@
 import io.agentscope.core.message.ContentBlock;
 import io.agentscope.core.message.TextBlock;
 import io.agentscope.core.message.ToolResultBlock;
+import io.agentscope.core.message.ToolResultState;
 import io.agentscope.core.message.ToolUseBlock;
 import io.agentscope.core.tool.test.SampleTools;
 import io.agentscope.core.tool.test.ToolTestUtils;
@@ -124,6 +125,20 @@ void shouldReturnErrorWhenToolThrows() {
                 "Error: Tool execution failed: Tool error: test failure",
                 content,
                 "Error message should be wrapped by executor");
+        assertEquals(
+                ToolResultState.ERROR,
+                responses.get(0).getState(),
+                "A failed tool call must be reported with state=ERROR, not SUCCESS");
+    }
+
+    @Test
+    @DisplayName("ToolResultBlock.error() carries state=ERROR (issue #2157)")
+    void errorResultCarriesErrorState() {
+        // Regression guard: previously error() left state=null (defaulting to
+        // RUNNING) and relied on an "[ERROR]" text prefix it never produced, so
+        // determineToolResultState() misclassified failures as SUCCESS.
+        ToolResultBlock result = ToolResultBlock.error("boom");
+        assertEquals(ToolResultState.ERROR, result.getState());
     }
 
     @Test