Sumly Chan Yuen Sum (born in 1958 in Hong Kong), is a social worker and politician in Hong Kong, who is a member of the Civic Party and a district councillor in Tsuen Wan District Council (Lei Muk Shue East). He has served as district councillor in Tsuen Wan since 1985.
In 2003, Chan claimed the name of "Tsuen Wan Election Union" headed by Albert Chan to take part in the District Council election, and renewed the seat successfully. In 2004, he joined Hong Kong Democratic Party and partnered with Lee Wing-tat, the former chairman of the Democratic Party to participate in the Hong Kong legislative election, 2004, but lost finally. In September 2007, he quit Democratic Party and joined Civic Party. In November 2007, he succeeded in keeping the seat of the district council. In 2008, Fernando Cheung and Chan represented Civic Party to participate in the Hong Kong legislative election, 2008, but both Cheung and he lost.