Toailoa's father wore a UCLA hat and a USC shirt to the ceremony.
"I was torn between the two, I couldn't really decide," Toailoa said. "I woke up this morning and wanted to be a Bruin."
Toailoa said he brought a USC hat to the ceremony in case he changed his mind.
The 6-foot, 215-pound linebacker is considered a top prospect in the 2016 class.
Toailoa said he felt student life at UCLA fit him best.
"Football is a business and coaches come and go," he said. "I took coaches out of the equation and could still see myself as a Bruin."
Toailoa can sign a letter of intent on Feb. 3, 2016.