Kang Yoon-sung (born November 16, 1983 in Goyang), better known by his stage name K, is a pop singer from South Korea under contract in Japan. After the failure of his first album in South Korea in 2004, K crossed over to Japan. His first Japanese album, Beyond the Sea, has achieved a sales of over 300,000 copies.

K put his musical activities on hold in 2010 so he could complete the Korean mandatory military service.