 <p>If the response is between 199 and 300 ( >= 200 and &lt; 300 ) or equal to 304 and the responseText can be successfully converted to the dataType that you provide (text by default), it is considered a successful request.</p> <p>For example, if you return JSON and you get a 200 response status but it fails, it is more than likely a JSON parser problem meaning your JSON is not valid.</p> <p>If you are returning HTML or XML and it fails with a 200 response status, the responsetext couldn't be converted to HTML or XML respectively (commonly happens in IE with invalid html/xml)</p>