The Sacramento Bee reports Yiannopoulos stood on a picnic table Saturday at the campus quad and used a megaphone to decry Friday's cancellation of planned speeches by him and former pharmaceutical executive Martin Shkreli.
Protesters used their own megaphone to periodically interrupt him.
Yiannopoulos then walked through the campus, followed by supporters and a loud group of counter-protesters chanting, "No Milo. No KKK. No fascist U.S.A."
Yiannopoulos writes for right-wing Breitbart News and is permanently banned from Twitter after leading a harassment campaign.
Shkreli was heavily criticized in 2015 for raising the price of a lifesaving malaria medication.
University police put up barricades as protesters shouting "shut it down" grew increasingly rowdy in the hours leading up to the Friday night talks. The UC Davis College Republicans, who sponsored the event, chose to cancel.
Yiannopoulos writes for right-wing Breitbart News and is permanently banned from Twitter after leading a harassment campaign against "Ghostbusters" actress Leslie Jones. He said on his Facebook page that the event was canceled after "violence from left-wing protesters."
But campus police said there was no violence or property destruction, and no arrests were made.
The school's Interim Chancellor Ralph Hexter said he was "deeply disappointed" by the protests and cancellation.