Locating Your Product Serial Number
Use any of these methods to find the serial number of your iMac:
ÂChoose Apple () from the menu bar and then choose About This Mac. Click the version number beneath the words “Mac OS X” to cycle through the Mac OS X version number, the build version, and the serial number.
ÂClick the Finder icon and open /Applications/Utilities/System Profiler. Click Hardware in the Contents pane.
ÂLook on the bottom of the iMac stand.