|Country (sports)|| United States|
|Born||June 27, 1976|
Los Angeles, California
|Plays||Right-handed (two-handed backhand)|
|Highest ranking||No. 72 (October 11, 1999)|
|Grand Slam Singles results|
|Australian Open||2R (1999, 2001)|
|French Open||2R (2001, 2002)|
|Wimbledon||1R (1999, 2001, 2002)|
|US Open||2R (1999)|
|Highest ranking||No. 102 (October 30, 2006)|
|Grand Slam Doubles results|
|US Open||1R (1996, 1999, 2000)|
Cecil Valdeavilla Mamiit (born June 27, 1976) is a former tennis player from the United States who went on to represent the Philippines. He began his professional career in 1996 and reached his highest individual ranking in the ATP Tour on October 11, 1999 as World No. 72.
Mamiit won the silver medal in the men's tournament at the 1999 Pan American Games in Winnipeg, Manitoba, Canada, after losing the final to fellow American Paul Goldstein. 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. 1 doubles players Mahesh Bhupathi and Leander Paes of India. He won the men's singles in the Ojai Tennis Tournament in 2008.
His best tournament result came at the 1999 San Jose tournament. As a qualifier he defeated Danish Kenneth Carlsen, Americans Andre Agassi (although Agassi was up 6-0, 6-6 before he defaulted), Australian Mark Woodforde, and another American Michael Chang before losing in the final to another Aussie Mark Philippoussis 6-3, 6-2.
Mamiit represented the Philippines Davis Cup team, where he was undefeated until 2008.
|Grand Slam (0)|
|Tennis Masters Cup (0)|
|ATP Masters Series (0)|
|ATP Tour (0)|
|ITF Titles (7)|
|1.||July 13, 1998||Aptos||Hard||Takao Suzuki||6-7, 6-3, 6-2|
|2.||November 9, 1998||Las Vegas||Hard||Maurice Ruah||7-5, 6-3|
|3.||November 23, 1998||Burbank||Hard||David Nainkin||7-6, 7-5|
|4.||December 6, 1999||Burbank||Hard||Alex O'Brien||7-5, 6-3|
|5.||May 31, 2004||Tallahassee||Hard||Björn Rehnquist||6-4, 4-6, 7-5|
|6.||May 30, 2005||Yuba City||Hard||Paul Goldstein||6-4, 6-4|
|7.||September 11, 2006||New Orleans||Hard||Amer Delic||6-3, 7-6|