Souza made his Strikeforce debut on December 19, 2009 at Strikeforce: Evolution with a first-round submission win over Matt Lindland, via arm-triangle choke. In this fight, Souza showed a major improvement in his stand up game and striking. Souza faced Joey Villaseñor on May 15, 2010 at Strikeforce: Heavy Artillery. He won the fight via unanimous decision, dominating the first round, being very aggressive, achieving the mount position and almost achieving the submission, but slowed down on the 2nd and 3rd round.