With a successful high school career, Dillashaw received a full-ride scholarship to wrestle for Cal State Fullerton Titans. In the 2005–06 season, Dillashaw's freshman year, he posted a 14–16 record including a 10–8 mark in dual matches. He went 3–4 in Pac-10 dual meets. Dillashaw traveled to Ukraine in the summer of 2006 to work on his wrestling skills. Dillashaw's sophomore season was a more successful one having an overall record of 17–14 with an 11–4 mark in duals, including 5–3 in the Pac-10. In April 2007, he placed sixth in the University Greco Wrestling Championships in Akron, Ohio, at 132.25 pounds. He also placed fourth at the Pac-10 championship in 2007.