Injection moulding process usually used in industry manufacturing for producing variety plastic parts. The most serious issues in manufacturing is to minimize the cost of producing product without influencing their final product quality. To produce a high quality of product, it's important to control the parameters of injection moulding machine. So that, this paper presents a systematic methodology to analyse on the quality (warpage) on a top part of optical mouse using Response Surface Methodology (RSM). Acrylonitrile Butadiene Styrene (ABS) were selected as a material that used in simulation. The variable parameters were selected based on previous researches that influence the warpage and shrinkage on the moulded part which are packing pressure, packing time, melt temperature, mould temperature and cooling time. The result show that the warpage on the top part of optical mouse was improved 28.4% after the optimization process. Mould temperature was selected as the most significant factors affects the warpage, followed by packing pressure and packing time.