How to get parent category Id in Magento

To get Parent Category Id you must know the current category Id, for that you need to write
<?php 
$_cat = new Mage_Catalog_Block_Navigation();
$curent_cat = $_cat->getCurrentCategory();
$curent_cat_id = $curent_cat->getId();?>
Now you can get Parent Category Id.
write the code given below to get the Id
<?php $parentId=Mage::getModel('catalog/category')->load($curent_cat_id)->getParentId();
echo $parentId; // $parentId will print your current category's parent Id
?>
Source:http://xhtmlandcsshelp.blogspot.in/2010/08/how-to-get-parent-category-id-in.html