In recent years, permanent magnet synchronous motors with concentrated winding and fractional slot had been widely used in servo control systems. Cyclic torque pulsation, which was detrimental to the speed and position regulation of a high performance servo system, existed in such type of motors due to poleslot combinations and imperfections in manufacturing such as mechanical errors introduced during parts machining and assembly. Therefore, an observer based torque ripple estimation and mitigation scheme was developed. Torque observer was adopted to estimate the torque ripple, and then torque ripple and position signal were processed to calculate the corresponding compensation torque current, which was in turn fedforward to the current command to suppress the resultant speed pulsation. Simulation and experiment results were obtained to verify the effectiveness of this method.