Fong Sai-yuk (Mandarin: Fang Shiyu) was a (possibly fictional) Chinese martial artist and folk hero from Zhaoqing, Guangdong province. He was first mentioned in wuxia stories dating from the Qing dynasty (1644–1912), such as Shaolin Xiao Yingxiong (少林小英雄; Young Hero of Shaolin), Wan Nian Qing (萬年青) and Qianlong You Jiangnan (乾隆游江南; The Qianlong Emperor Visits Jiangnan). His father, Fong Tak (Mandarin: Fang De), was a wealthy merchant, while his mother, Miu Tsui-fa (Mandarin: Miao Cuihua), was a martial arts expert. Fong Sai-yuk was also associated with Hung Hei-gun (Mandarin: Hong Xiguan) and the Five Elders of the Southern Shaolin Monastery.
Stories about Fong Sai-yuk have been adapted into films and television series since the 1970s. The most notable ones are the 1993 Hong Kong film Fong Sai-yuk and its sequel, which starred Jet Li.