Kanstantsin Sivtsov (or Siutsou (Belarusian: Канстанцін Віктаравіч Сіўцоў; Łacinka: Kanstancin Viktaravič Siŭcoŭ; born 9 August 1982) is a Belarusian former professional road bicycle racer, who rode professionally between 2001 and 2018 for the Itera, Lokomotiv, Fassa Bortolo, Acqua & Sapone, Barloworld, HTC–Highroad, Team Sky, Team Dimension Data and Bahrain–Merida squads. He retired after provisionally being suspended from the sport following an adverse analytical finding for erythropoietin (EPO).