Can I update both of my mac with the single purchase of OSX I would like to purchase OSX 10.8(Mountain Lion) using my apple account.

The question is am having two mac computers with snow leopard, Can I update both of my mac with the single purchase?

any help?
Yes. With one purchase you can uptate all your macs that are linked to your iTunes account you own. 

How to upgrade to 10.8 on Apple.com.