diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 57a8df29fe68..d2a2aeaa643f 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -347952,6 +347952,12 @@
      {}
     ]
    ],
+   "html/semantics/forms/the-textarea-element/textarea-textLength.html": [
+    [
+     "/html/semantics/forms/the-textarea-element/textarea-textLength.html",
+     {}
+    ]
+   ],
    "html/semantics/forms/the-textarea-element/textarea-type.html": [
     [
      "/html/semantics/forms/the-textarea-element/textarea-type.html",
@@ -587323,6 +587329,10 @@
    "5f5932aeba8a0a7da66ee006a6e604780210d57b",
    "testharness"
   ],
+  "html/semantics/forms/the-textarea-element/textarea-textLength.html": [
+   "0f9b8cdaace12d4f4e7fbd57a90fcba7e826ced5",
+   "testharness"
+  ],
   "html/semantics/forms/the-textarea-element/textarea-type.html": [
    "81a270bc3c9304f8b2e7dd526519f4eab7d94f45",
    "testharness"
diff --git a/testing/web-platform/tests/html/semantics/forms/the-textarea-element/textarea-textLength.html b/testing/web-platform/tests/html/semantics/forms/the-textarea-element/textarea-textLength.html
new file mode 100644
index 000000000000..d249278960e9
--- /dev/null
+++ b/testing/web-platform/tests/html/semantics/forms/the-textarea-element/textarea-textLength.html
@@ -0,0 +1,19 @@
+<!DOCTYPE HTML>
+<title>The textLengh IDL attribute</title>
+<meta content="charset=utf-16">
+<link rel="author" title="tigercosmos" href="mailto:phy.tiger@gmail.com">
+<link rel="help" href="https://html.spec.whatwg.org/multipage/#dom-textarea-textlength">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<textarea id="textarea"></textarea>
+<script>
+    var textarea = document.getElementById("textarea");
+
+    test(function () {
+        textarea.value= "Hello, World!";
+        assert_equals(textarea.textLength, 13);
+
+        textarea.value = "\u4f60\u597d\uff0c\u4e16\u754c\uff01"; //你好，世界!
+        assert_equals(textarea.textLength, 6);
+    }, "Textarea's 'testLength' should work for utf-16.");
+</script>
\ No newline at end of file
