J1.5:Restricting access to a Category
From Joomla! Documentation
This article is for Joomla! CMS Version(s) 
To restrict access to a category:
- Login to the administrative back end.
- Get into the Category Manager by either:
- Selecting Category Manager from the Site Control Panel, or
- Navigating to Content > Category Manager using the menu bar.
- In the Category Manager:
- Go to the category of interest and repeatedly click in the Access Level column until the desired access level appears.
- That's it.