Abstract: In the present study the effect of aging treatment on the superelastic behavior and transformation temperatures of NiTi shape memory alloy was studied. The wire with composition of Ti-50.5 at.% Ni was prepared via VAR and rolling followed homogenization. After solution annealing, aging treatment was carried out at 400 and 500 °C for 30 and 60 min. Three point bending test was used to investigate the superelastic behavior and transformation temperatures was determined by differential scanning calorimetry. It was found that the superelastic characteristics including level of bending stress on louding and unloading, mechanical hysteresis, slope of plateau and amount of permanent deflection are sensitive to aging treatment. Also, transformation temperatures and thermal hysteresis change and R phase appears as result of this treatment.