Number of blades of torque converter elements plays an important role in the design and performance of torque converters. In this paper, effects of the number of pump and turbine blades on the performance of torque converters are investigated numerically at different speed ratios, using a commercial software, ANSYS-CFX. Two torque converters, with the same outer diameter of 245 mm, were studied. Number of blades of the first torque converter is (32, 36 and 17) and for the second torque converter is (41, 37 and 17) for the pump, turbine and stator respectively. Blade shape and angles for the torque converter elements are the same. Numerical simulation results were compared and verified with the available literature and experimental results. A satisfactory agreement is presented between numerical and experimental results. Results showed that increasing the number of the blades of both of the pump and the turbine caused an increase of both of pump and turbine torque while the stall torque ratio is decreased and the coupling point occurred at lower speed ratio. Also, increasing the number of blades caused the maximum efficiency to be decreased. This may be explained by the change of slip factor of different number of blades as well as the effect of friction on shock losses. The study showed that there is an optimum number of blades required to improve the performance of torque converter.