The purpose of this paper is to evaluate of braking characteristics for disc brake rotor diameter. First, selected two types of disc brake rotor for Ø232 and Ø256. In addition to the discs, the specifications of all the parts such as the caliper and the hydraulic device are same. Second, the brake dynamometer was used to perform the 300Cycle test in the torque durability mode, the OEM standard of the automobile manufacturer. The total test time is 96 hours per sample. Third, braking characteristics were evaluated by braking distance, fade, brake torque variation(BTV) and cooling performance. Finally, checked the presence of defects by inspecting the sample through liquid penetrant testing.