Otto Kemppainen (born 27 October 2003) is a Finnish professional footballer who plays as a defender for Veikkausliiga club AC Oulu and the Finland U21 national team.
Born in Rovaniemi, Kemppainen started his playing career in Rovaniemen Palloseura (RoPS). After a short stint in Hellas Verona academy in 2022, Kemppainen signed a professional contract with Veikkausliiga club SJK Seinäjoki on 26 July 2022, on a deal until the end of 2024.
On 4 November 2024, Kemppainen signed with AC Oulu in Veikkausliiga on a two-year deal with a one-year option.