Following are the few limitations of Ajax -
1. Only recent browsers that support the XMLHttpRequest Javascript object are able to correctly interpret an AJAX page.
2. Search engines may not be able to index all content published with AJAX.
3. Back functionality cannot work because the dynamic pages don’t register themselves to the browsers history engine. Hence the need of Iframe becomes essential.
4. The page cannot be bookmarked if implemented using Ajax.
5. If java script is disabled , Ajax will not work.