No, you don't need Leopard. You can to directly to Snow Leopard then to Mountain Lion. Or yhou can stop at Lion.
Upgrading to Mountain Lion
You can upgrade to Mountain Lion from Lion or directly from Snow Leopard. Mountain Lion can be downloaded from the Mac App Store for $19.99. To access the App Store you must have Snow Leopard 10.6.6 or later installed.
If you need to purchase Snow Leopard contact Customer Service: Contacting Apple for support and service. The price is $29.00 plus tax. You will receive physical media - DVD - by mail.
Third-party sources for Snow Leopard are:
After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store.
If you need to purchase Lion contact Customer Service: Contacting Apple for support and service. The cost is $19.99 (as it was before) plus tax. It's a download.
Be sure your computer meets the minimum requirements:
Macs that can be upgraded to OS X Mountain Lion
- iMac (Mid 2007 or newer)
- MacBook (Late 2008 Aluminum, or Early 2009 or newer)
- MacBook Pro (Mid/Late 2007 or newer)
- MacBook Air (Late 2008 or newer)
- Mac mini (Early 2009 or newer)
- Mac Pro (Early 2008 or newer)
- Xserve (Early 2009)
Are my applications compatible?
For a complete How-To introduction from Apple see Apple - Upgrade your Mac to OS X Mountain Lion.