Cecil Valdeavilla Mamiit (born June 27, 1976) is a former tennis player from the United States who went on to represent the Philippines.

In 1996, he won the NCAA singles championship as an USC freshman, a feat that had not been achieved since John McEnroe attended Stanford University in 1978.

At the 2006 Asian Games held in Doha, Qatar, he won bronze in the singles event after losing in the semifinals to Lee Hyung Taik of South Korea.

In the doubles event, he also won bronze, along with fellow Filipino-American tennis player Eric Taino, losing to the first-seeded and former World no.

From January 2011 through the clay court season, he was the hitting partner for Russian Maria Sharapova, where she won the 2012 French Open to complete her Career Grand Slam.