how to lock a folder in the mac computer?

Answer 1

Select your folder from the Finder, File to Get Info. Ownership & Permissions, click on the triangle next to Details, and then click the lock icon and Wha-la! You're folder is now locked!

That will lock your folder from being changed by your system such as like when you run a repair disk or from other users so they can't claim the folder/file as their own and then block you out, but I'm guessing that's not exactly what you're looking for.

I'm guessing that you're trying to lock personal documents up in a folder so that they can't be seen by people that access your computer on your account. Although the ideal thing to do would be to create a seperate account for a guest, you can still prevent people from viewing the contents of that folder while logged into your account. What you have to do is "trick" your computer into thinking that the folder doesn't belong to you. Here's how:

Select the folde.
File > Get Info
Ownership and Permissions > Details
If it is locked, unlock it
Work from bottom to top:
Change Others to No Access
Change Group to whatever (i like system) and select No Access
Under Owner, change the Access to "No Access" and then change the group to whatever (same as above)
You will then have to type in your Administrator Password
Close the info window

This will block "you" (or that other person that is logged in as you) from viewing the contents of that folder, unless you put in a password. Now, the thing doesn't go into effect immediately, but takes a few minutes from last time you put in your password (so you're not typing in your password 1000 times while doing admin. stuff), but then it will be "locked"

To unlock, just bring back the info window, and give yourself permission on the Owner part only, then enter your password.

I also found an application that makes things a little easier:
http://www.apimac.com/secret_folder/index.php