diff --git a/docs/rules/no-private-in.md b/docs/rules/no-private-in.md
new file mode 100644
index 00000000..a25adb9d
--- /dev/null
+++ b/docs/rules/no-private-in.md
@@ -0,0 +1,24 @@
+# es/no-private-in
+> disallow `#x in obj`
+
+- ✅ The following configurations enable this rule: `plugin:es/no-new-in-esnext`
+
+This rule reports ES2022 private in (`#x in obj`) as errors.
+
+## Examples
+
+⛔ Examples of **incorrect** code for this rule:
+
+<eslint-playground type="bad" code="/*eslint es/no-private-in: error */
+class A {
+    #x;
+    fn () {
+        var hasX = #x in obj;
+    }
+}
+" />
+
+## 📚 References
+
+- [Rule source](https://github.com/mysticatea/eslint-plugin-es/blob/v4.1.0/lib/rules/no-private-in.js)
+- [Test source](https://github.com/mysticatea/eslint-plugin-es/blob/v4.1.0/tests/lib/rules/no-private-in.js)
diff --git a/lib/rules/no-private-in.js b/lib/rules/no-private-in.js
new file mode 100644
index 00000000..051d43b5
--- /dev/null
+++ b/lib/rules/no-private-in.js
@@ -0,0 +1,41 @@
+/**
+ * @author Yosuke Ota <https://github.com/ota-meshi>
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "disallow `#x in obj`.",
+            category: "ES2022",
+            recommended: false,
+            url:
+                "http://mysticatea.github.io/eslint-plugin-es/rules/no-private-in.html",
+        },
+        fixable: null,
+        messages: {
+            forbidden:
+                "ES2022 private in (`#{{private}} in {{object}}`) is forbidden.",
+        },
+        schema: [],
+        type: "problem",
+    },
+    create(context) {
+        return {
+            "BinaryExpression[operator='in'] > PrivateIdentifier.left"(node) {
+                context.report({
+                    node,
+                    messageId: "forbidden",
+                    data: {
+                        private: node.name,
+                        object:
+                            node.parent.right.type === "Identifier"
+                                ? node.parent.right.name
+                                : "object",
+                    },
+                })
+            },
+        }
+    },
+}
diff --git a/package.json b/package.json
index 5b10b719..e05812cd 100644
--- a/package.json
+++ b/package.json
@@ -20,11 +20,11 @@
     "@mysticatea/eslint-plugin": "^13.0.0",
     "@typescript-eslint/parser": "^4.8.2",
     "@vuepress/plugin-pwa": "^1.2.0",
-    "acorn": "^7.1.0",
+    "acorn": "^8.5.0",
     "codecov": "^3.8.1",
-    "eslint": "^7.10.0",
+    "eslint": "^8.0.0-0",
     "eslint4b": "^7.10.0",
-    "espree": "^7.0.0",
+    "espree": "^9.0.0",
     "globals": "^12.0.0",
     "mocha": "^6.2.0",
     "npm-run-all": "^4.1.5",
diff --git a/tests/lib/rules/no-private-in.js b/tests/lib/rules/no-private-in.js
new file mode 100644
index 00000000..ef6ea090
--- /dev/null
+++ b/tests/lib/rules/no-private-in.js
@@ -0,0 +1,36 @@
+/**
+ * @author Yosuke Ota <https://github.com/ota-meshi>
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+const RuleTester = require("../../tester")
+const rule = require("../../../lib/rules/no-private-in.js")
+
+if (!RuleTester.isSupported(2022)) {
+    //eslint-disable-next-line no-console
+    console.log("Skip the tests of no-private-in.")
+    return
+}
+
+new RuleTester().run("no-private-in", rule, {
+    valid: [
+        "class A { f(obj) { return '#x' in obj } }",
+        "class A { f(obj) { return x in obj } }",
+        "class A { #x; f(obj) { return foo in obj.#x } }",
+    ],
+    invalid: [
+        {
+            code: "class A { #x; f(obj) { return #x in obj } }",
+            errors: ["ES2022 private in (`#x in obj`) is forbidden."],
+        },
+        {
+            code: "class A { #x; f(obj) { return #x in obj.foo } }",
+            errors: ["ES2022 private in (`#x in object`) is forbidden."],
+        },
+        {
+            code: "class A { #x; f(obj) { return #x in obj.#x } }",
+            errors: ["ES2022 private in (`#x in object`) is forbidden."],
+        },
+    ],
+})