A piston is an important component of the shock absorber which determines comfortable riding and han­dling. Conventional piston is made of metal powder that is pressed in a mold, and then sintered at high tem­peratures below the melting point before machining processes such as drilling, sizing and teflon banding. This study aims at cutting down cost and weight, and improving the process by replacing the traditional sint­ering process used for manufacturing the shock absorber with the injection molding process adopting en­gineering plastics as raw material. To analyze the injection molding process, we used the commercial pro­gram, MOLDFLOW, and obtained an optimal combination of the process parameters. In addition, by com­paring the engineering plastic piston with the metal powder piston through the formability and the per­formance experiments, we confirmed the availability of this alternative process suggested.