Use strip_tags();
strip_tags ($str, '<p><div>');
this line will remove all the tags but P and DIV You can add more alowable tags to second argument.
Example from php.net
<?php
$text = '<p>Test paragraph.</p><!-- Comment --> <a href="#fragment">Other text</a>';
echo strip_tags($text);
echo "\n";
// Allow <p> and <a>
echo strip_tags($text, '<p><a>');
?>
The above example will output:
Test paragraph. Other text
<p>Test paragraph.</p> <a href="#fragment">Other text</a>