Company ABC is a manufacturing company and committed to providing high-quality metal stamping and plastic injection molding products. The main objective of the study is to reduce the black spot defects in Case Lower (68 MB62) that occurred in the plastic injection molding process. The researcher used Lean Six Sigma Methodology as a technique to reduce quality problems. Applied research was used as the research design in the study. Based on the findings of the study, the problem occurred in the filtering process and as a result, black spot defects had the highest defect percentage equivalent to 7.85%. The overall current process performance or Process Z was 1.42 lower than the standard value of 2.00. Further validation was made using Why-why analysis and found out that filter mesh design was the identified root cause of the problem. To reduce the percentage of defects, improvement of filter mesh design was completed and after implementation, the data was collected and based on the results the defect percentage was reduced to 2.16%, overall process performance or Process Z increased to 2.02 higher than the minimum limit of 2.00. For the improvement to be sustained, a work instruction and control plan was developed.