http://www.mixedmartialarts.com/news...-for-one-bout/

Today during a Google Hangout, UFC President Dana White was asked what the most any UFC athlete had ever made for a single bout. Lorenzo Fertita happen to be near by and they both agreed it was approxiamately $5 million. The UFC bosses would not reveal to whom it was paid, but Georges St-Pierre, Anderson Silva, or Brock Lesnar are likely candidates:

"We paid a guy $5 million for a fight before, [but] we didn't start making money until 2007. That was six years ago. So boxing's been around for a 100 years, they've been doing big events since way back when. Pretty amazing what we have done in short amount of time. I don't think a lot of people look at that way and break it down for what it really is."