diff --git a/index.js b/index.js
index cb95535..ce70e9b 100644
--- a/index.js
+++ b/index.js
@@ -212,6 +212,17 @@ class assertWrapper extends Helper {
       assert.fail(`String ${actual} doesn't contain substring ${substring}`);
     }
   }
+
+  /**
+   * Check that string does not contain substring
+   * @param {string} actual
+   * @param {string} substring
+   */
+  assertStringNotIncludes(actual, substring) {
+    if (actual.indexOf(substring) > 0) {
+      assert.fail(`String ${actual} contains substring ${substring}`);
+    }
+  }
 }
 
 module.exports = assertWrapper;
diff --git a/readme.md b/readme.md
index ca8dc8a..bcf5199 100644
--- a/readme.md
+++ b/readme.md
@@ -262,4 +262,16 @@ I.assertStringIncludes('mystring'. 'str');
 -   `actual` - tested string
 -   `substring` - expected substring
 
+## assertStringNotIncludes
+
+Check that string does not contain substring
+
+```js
+I.assertStringNotIncludes('mystring', 'sym');
+```
+
+**Parameters**
+
+-   `actual` - tested string
+-   `substring` - not expected substring