i am already using OX mountain Lion, but since i noticed that my laptop is getting slower i want to re-install the previous OS, which is OS X Lion... is it possible to re-install it? need your help. thanks

Only if you have kept a copy of the Lion installer application. You will also have to first erase the hard drive.

Or, restore from a Time Machine backup.

A complete erasure of your hard disk is required either way.

Yes there is IF your Mac originally came with Lion.

Or if you installed Lion over the top of Snow Leopard.

With either you will lose all the data on the drive so before you do this make sure you have backups, Copies, of all your personal files and backups, Copies, of any downloaded software programs you have installed along with the License Keys to those programs.

So the first question is did your Mac come with Lion Preinstalled?

But it is easier to diagnose your problem and fix it then revert back to Lion. Use this article to help. http://www.reedcorner.net/understanding-upgrade-nightmares/

Then try this instead:

Reinstalling Lion/Mountain Lion Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.

Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

My early 2008 MBPro was really pokey after the upgrade from SL. Turned off iCloud completely, which returned it to a reasonable level of normalness, except for the reallllllly slloooooowww startup. I can boot my Windows 7 bootcamp partition 4 times in the time it takes for ML to start.

Too many issues with Mail (still crap), Calendar (really screwed up with time zones and generating double appointments). Back to using Entourage for my email, appointments, etc.

Jimbudz wrote:

Yes, it's originally a LION OS X... actually i just bought my macbook pro three months ago.

Since your Mac came with Lion you will need to use Internet Recovery. That is were you boot the computer from over the internet and that will allow you to reinstall Lion on your system.

At startup you halod down Command+Option+r keys until you see a spinning globe in the center of the screen.

Once it loads completely you can use Disk Utility to re-partition the drive as one partition and then reinstall Mac OS X.