diff --git a/agentscope-harness/src/main/java/io/agentscope/harness/agent/filesystem/remote/RemoteFilesystem.java b/agentscope-harness/src/main/java/io/agentscope/harness/agent/filesystem/remote/RemoteFilesystem.java
index 57efde917d..e6131d5213 100644
--- a/agentscope-harness/src/main/java/io/agentscope/harness/agent/filesystem/remote/RemoteFilesystem.java
+++ b/agentscope-harness/src/main/java/io/agentscope/harness/agent/filesystem/remote/RemoteFilesystem.java
@@ -33,6 +33,9 @@
 import io.agentscope.harness.agent.filesystem.remote.store.StoreItem;
 import io.agentscope.harness.agent.filesystem.util.FilesystemUtils;
 import io.agentscope.harness.agent.workspace.WorkspaceIndex;
+import java.nio.ByteBuffer;
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.CodingErrorAction;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
@@ -503,9 +506,15 @@ public List<FileUploadResponse> uploadFiles(
             String contentStr;
             String encoding;
             try {
-                contentStr = new String(content, StandardCharsets.UTF_8);
+                contentStr =
+                        StandardCharsets.UTF_8
+                                .newDecoder()
+                                .onMalformedInput(CodingErrorAction.REPORT)
+                                .onUnmappableCharacter(CodingErrorAction.REPORT)
+                                .decode(ByteBuffer.wrap(content))
+                                .toString();
                 encoding = "utf-8";
-            } catch (Exception e) {
+            } catch (CharacterCodingException e) {
                 contentStr = Base64.getEncoder().encodeToString(content);
                 encoding = "base64";
             }
diff --git a/agentscope-harness/src/test/java/io/agentscope/harness/agent/filesystem/RemoteFilesystemCASTest.java b/agentscope-harness/src/test/java/io/agentscope/harness/agent/filesystem/RemoteFilesystemCASTest.java
index d8a4f676f4..5c6d7b1ffc 100644
--- a/agentscope-harness/src/test/java/io/agentscope/harness/agent/filesystem/RemoteFilesystemCASTest.java
+++ b/agentscope-harness/src/test/java/io/agentscope/harness/agent/filesystem/RemoteFilesystemCASTest.java
@@ -218,6 +218,24 @@ void uploadFiles_repeatedOnSamePath_returnsSuccessEachTime() {
         assertEquals("iter-4", read.fileData().content());
     }
 
+    @Test
+    void uploadFiles_nonUtf8Binary_roundTripsWithoutCorruption() {
+        InMemoryStore store = new InMemoryStore();
+        RemoteFilesystem fs = newFs(store);
+        byte[] expected = new byte[] {0, (byte) 0xff, 1, (byte) 0x80};
+
+        List<FileUploadResponse> upload =
+                fs.uploadFiles(CTX, List.of(Map.entry("/image.png", expected)));
+        assertEquals(1, upload.size());
+        assertTrue(upload.get(0).isSuccess(), () -> "upload failed: " + upload.get(0).error());
+
+        var download = fs.downloadFiles(CTX, List.of("/image.png"));
+        assertEquals(1, download.size());
+        assertTrue(
+                download.get(0).isSuccess(), () -> "download failed: " + download.get(0).error());
+        assertArrayEquals(expected, download.get(0).content());
+    }
+
     @Test
     void downloadFiles_decodesWrappedBase64Content() {
         InMemoryStore store = new InMemoryStore();