Abstract : Nickel-titanium rotary endodontic instruments have clinical advantages in endodontic treatment especially for curved root canals. In daily clinical settings, Ni-Ti instruments are heat-sterilized by autoclave and sometimes chemically disinfected by soaking in NaClO solution. The aim of this study was to evaluate the influence of autoclave heat sterilization and NaClO chemical disinfection on the mechanical properties of Ni-Ti rotary instruments using a bending test and differential scanning calorimetry (DSC). Three types of Ni-Ti rotary instruments, ProFile^®.06tapers, ProFile^® Series 29, and ProFile^® Orifice Shaper, as well as a and stainless-steel hand K-file, were used in this study. From the results of the bending test, there was no significant difference in bending load among all groups. The bending load of nickel-titanium alloy did not change by autoclave heat sterilization at 121°C or by 6% NaClO chemical disinfection. From the results of DSC, the austenitic transformation finishing temperature (A_f) point after each sterilizing procedure did not change and remained lower than 37°C, which was suitable to exhibit super-elasticity. The mechanical properties of the nickel-titanium rotary endodontic instruments were not significantly affected by autoclave heat sterilization (121°C, 2 atm) or by 6% NaClO chemical disinfection for 30 minutes. Therefore, the sterilizing procedures for nickel-titanium instruments, including autoclave heat sterilization and NaClO chemical disinfection, may be less influential compared to their history of use when discarding the instruments.