diff --git a/docs/_static/css/custom_log.css b/docs/_static/css/custom_log.css
index 61f65d019..57d0cf6d1 100644
--- a/docs/_static/css/custom_log.css
+++ b/docs/_static/css/custom_log.css
@@ -27,3 +27,27 @@ div.output_area.stderr {
 div.output_area.stdout {
     color: #d3d3d3 !important;
 }
+
+.sglang-docs-deprecation-banner {
+    background: #fff4cc;
+    border-bottom: 1px solid #d8a21f;
+    color: #2f2a1f;
+    font-size: 0.95rem;
+    line-height: 1.45;
+    overflow-wrap: anywhere;
+    padding: 0.75rem 1.25rem;
+    position: relative;
+    text-align: center;
+    z-index: 1030;
+}
+
+.sglang-docs-deprecation-banner a {
+    color: #1f5fbf;
+    font-weight: 600;
+    text-decoration: underline;
+}
+
+.sglang-docs-deprecation-banner a:focus,
+.sglang-docs-deprecation-banner a:hover {
+    color: #143f80;
+}
diff --git a/docs/_static/js/deprecation_banner.js b/docs/_static/js/deprecation_banner.js
new file mode 100644
index 000000000..87c8d73fa
--- /dev/null
+++ b/docs/_static/js/deprecation_banner.js
@@ -0,0 +1,49 @@
+(function () {
+    "use strict";
+
+    var oldOrigin = "https://sgl-project.github.io";
+    var newOrigin = "https://docs.sglang.io";
+
+    function buildNewDocsUrl() {
+        var href = window.location.href;
+
+        if (href === oldOrigin || href.indexOf(oldOrigin + "/") === 0) {
+            return href.replace(oldOrigin, newOrigin);
+        }
+
+        return newOrigin + window.location.pathname + window.location.search + window.location.hash;
+    }
+
+    function addDeprecationBanner() {
+        if (document.getElementById("sglang-docs-deprecation-banner")) {
+            return;
+        }
+
+        var link = document.createElement("a");
+        link.href = buildNewDocsUrl();
+        link.textContent = link.href;
+
+        var banner = document.createElement("div");
+        banner.id = "sglang-docs-deprecation-banner";
+        banner.className = "sglang-docs-deprecation-banner";
+        banner.setAttribute("role", "status");
+        banner.setAttribute("aria-live", "polite");
+
+        var prefix = document.createTextNode(
+            "This legacy documentation site will be deprecated soon. Please use the new SGLang documentation at "
+        );
+        var suffix = document.createTextNode(".");
+
+        banner.appendChild(prefix);
+        banner.appendChild(link);
+        banner.appendChild(suffix);
+
+        document.body.insertBefore(banner, document.body.firstChild);
+    }
+
+    if (document.readyState === "loading") {
+        document.addEventListener("DOMContentLoaded", addDeprecationBanner);
+    } else {
+        addDeprecationBanner();
+    }
+})();
diff --git a/docs/conf.py b/docs/conf.py
index d6ca64d88..6140b47f8 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -131,6 +131,7 @@ html_context = {
 
 html_static_path = ["_static"]
 html_css_files = ["css/custom_log.css"]
+html_js_files = ["js/deprecation_banner.js"]
 
 
 def setup(app):
diff --git a/scripts/ci/check_no_docs_changes.py b/scripts/ci/check_no_docs_changes.py
index fb302439b..9ab5f32ae 100755
--- a/scripts/ci/check_no_docs_changes.py
+++ b/scripts/ci/check_no_docs_changes.py
@@ -13,6 +13,12 @@ The documentation has been migrated. Please make documentation updates in the
 corresponding location under docs_new/ instead.
 """
 
+LEGACY_DOCS_ALLOWLIST = {
+    "docs/_static/css/custom_log.css",
+    "docs/_static/js/deprecation_banner.js",
+    "docs/conf.py",
+}
+
 
 def staged_paths() -> list[str]:
     result = subprocess.run(
@@ -33,7 +39,10 @@ def staged_paths() -> list[str]:
 def main() -> int:
     paths = sys.argv[1:] or staged_paths()
     docs_paths = sorted(
-        path for path in paths if path == "docs" or path.startswith("docs/")
+        path
+        for path in paths
+        if (path == "docs" or path.startswith("docs/"))
+        and path not in LEGACY_DOCS_ALLOWLIST
     )
 
     if not docs_paths: