In this paper, Lean and Six Sigma were applied to a Small and Medium-Sized Enterprise (SME), Company XYZ for plastic manufacturing in Kuwait, to reduce the variation in their injection molding process. Variation exists within any process and when this variation goes beyond certain limits, non-conforming parts are produced and the company will face increased percentage of waste, operational cost, and reduced customer’s satisfaction. Many of the XYZ Company plastic fittings were rejected as they were defective or having defects such as internal surface marks, flash, and bubbles. Floor Traps 6x4x2 fittings accounted for the highest rejection rate in XYZ Company. Six Sigma DMAIC combined with the 5S were applied to tackle this problem. DMAIC is a general engineering design approach that can be applied for many production or service problems that need practical solutions. It is an acronym stands for Define, Measure, Analyze, Improve, and Control. Results show that by implementing Six Sigma combined with the 5S program, Company XYZ achieved an improvement in its Sigma Level and Defects rate (DPMO) which lead to significant cost savings and increased its competitiveness.