This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Yes, if it is a Macintosh ADB mouse. The "teardrop" ADB Mouse II that comes on newer Macs works great on the IIGS and can be found for a few bucks in Mac for-sale groups. Third party ADB mice should work too. Note: Mice for Mac Plus and before are not ADB so won't work. Mice for the new iMac won't work because they are for the USB interface. By: David Empson and David Wilson