Knut Østby (12 November 1922 – 6 August 2010) was a Norwegian sprint canoeist who competed from the late 1940s to the late 1950s. Participating in three Summer Olympics, he won a silver medal in the K-2 10000 m event at London in 1948 and another in the K-2 1000 m event at the 1950 World Championships.