By default Joomla! strip iframe tags in articles. to prevent stripping of iframe tags follow this steps :
- Log into your Joomla 2.5 Admin area
- In the top menu, hover over Extensions and click Plug-in Manager
- From the Select Type filter, choose editors
- From the list of editors, click on Editor - TinyMCE
- From the list of Basic Options, remove iframe from Prohibited Elements
- Click Save in the top right menu. Now you can add iframe tags to your articles and they should not be stripped.