In this research paper, six sigma DMAIC is applied in a plastics company to reduce the process variation in injection moulding process. When variation goes beyond a certain limit the level of non- conformity increases and poor-quality parts are produced. Company faces high percentage of wastage, production cost and low customer's satisfaction. The Company has many rejections due to hard fitting, black dots, air bubbles and flow marks. Car side mirror cover hard fitting and black dots are accounted as major defects in plastic industry. Six-sigma DMAIC was applied to overcome these problems. DMAIC is an engineering technique that can be used in service and production problems that require a practical solution. DMAIC is (D) Define, (M) Measure, (A) Analyse, (I) Improve, and (C) Control. Outcomes show that by implementing six sigma DMAIC, the company achieved a significant improved in its Defects rate (DPMO) and Sigma Level that prime to substantial cost reserved and improved its keenness. The main purpose of this research is first one to recognize the root cause of black dots and hard fitting as well as other surface marks in car side mirror plastic cover. The second purpose is to implement sigma DMAIC to improve the quality of car side mirror plastic cover.