The gameplay of UFC 2009 Undisputed is centered around striking and grappling styles. The game features three striking styles (Boxing, Kickboxing, Muay Thai) and three grappling styles (Wrestling, Judo, Brazilian Jiu-Jitsu), with each fighter carrying one style of each category. Simulating the likeness of UFC, two fighters go head-to-head in the Octagon using their suggested striking and grappling styles as well as signature moves commonly seen respective to each fighter.
The game offers a variety of modes for players to enjoy. Exhibition mode allows players to jump straight into gameplay with their favorite fighter. Classic Fights feature some of the most memorable fights available for replication in the player's hands, with unlocked montage videos showing highlights of the respective fight if completed as in real life. Players can also create their own fighter using Create-A-Fighter and potentially build their own career by uploading their created fighter into Career mode.