The largest amount of latent heat of the martensitic transformation in nickel titanium shape memory alloy was explored. The measured amounts of heat in the alloys with different compositions between 48.0 at.% Ni and 51.0 at.% Ni were compared. The largest amounts of -37.8 J/g in absorption and 34.8 J/g in emission were obtained as the averaged values of several samples with equiatomic composition. These magnitudes are close to those of novel heat storage ceramics, VO2 (51 J/g) and Ti3O5 (60 J/g), suggesting the NiTi alloy is potential candidate for heat storage material.