The California Gurls hitmaker was spotted cheering in the audience as her younger sibling took the stage for a showcase at the Bootsy Bellows venue in support of his new single Chained.
Perry attended the event with her parents Keith and Mary, as well as her older sister Angela.
A source tells EOnline.com: "Katy is so proud of David. She was screaming out her support and had a really great time. It is a very supportive family."
Perry wasn't the only star in attendance - David Arquette, Mary-Kate Olsen, Paris Hilton and her ex-boyfriend Good Charlotte rocker Benji Madden were also in the crowd.