A 56-year-old female had a severely calcified mitral valve annulus and a huge subvalvular mass. To avoid critical damages of the coronary artery and left ventricle, the annular calcification and the part of the mass adherent to the left ventricle were not resected. Then we performed mitral valve replacement using SuMit valve and collared reinforcement technique with xenopericardium without any major complications. The SuMit valve is designed to be placed in a supraannular position, and is useful to prevent valves from getting stuck.