This study investigates the effect of runner system design on tooth profile deformation in the injection molding simulation of plastic gears. Eight runner configurations were evaluated by varying the number and position of pin gates, while maintaining consistent gear geometry, material, and processing parameters. The simulation results showed that the runner layout significantly influences total deformation, residual stress distribution, and the geometric accuracy of molded gear teeth. Configurations with asymmetric or unbalanced flow paths led to increased warpage and internal stress, especially in gears with complex structural features. Among all proposed designs, the configuration with three symmetrically positioned pin gates along the gear rim achieved the optimal results, reduced dimensional deviations and better kept the original tooth profile. This arrangement enabled balanced melt flow and uniform shrinkage, which helped maintain the accuracy of the tooth profile. The findings demonstrate that optimizing gate placement, without changing the part design or processing conditions, can effectively improve the dimensional stability and performance of injection molded plastic gears.