How can I lock a folder in c#?

Hi.I want to lock my folder with c#? How can I do it?

Not sure what you mean by lock a folder.  Do you want to hide a folder in the file system?  Make it read-only?  Prevent permission access for a particular group?

I mean make it read-only.

You can set the Attributes on a file using DirectoryInfo
http://msdn.microsoft.com/en-us/library/system.io.directoryinfo_properties.aspx
 
DirectoryInfo directoryInfo = new DirectoryInfo(@"c:\temptest");
directoryInfo.Attributes = directoryInfo.Attributes | FileAttributes.ReadOnly;
Unfortunately this won't really do much, because there is not much meaning to setting a directory to readonly.  You more likely want to limit write access to a user or group of users through Active Directory.  Below is a link on codeproject that tells you how to do almost anything you can think of to restricting permissions to a directory:
http://www.codeproject.com/KB/system/everythingInAD.aspx