This study successfully applied the Lean Six Sigma DMAIC methodology to tackle quality and efficiency issues in a knit garment factory. Focusing on a polo shirt production line, we used the structured DMAIC (Define-Measure-Analyze-Improve-Control) approach to identify and solve key problems. Our investigation began with a Pareto analysis, which pinpointed the seven most critical sewing defects. We then used Fishbone diagrams to dig deeper, uncovering root causes like blunt needles and insufficient operator training. In response, we implemented targeted Kaizen, such as retraining operators and standardizing machine maintenance, guided by the PDCA cycle. The outcome of these efforts was a clear and positive improvement. Most notably, the defect rate fell substantially from 24.26% to 15.54%. At the same time, daily production rose from 796 to 863 pieces, and line efficiency improved from 36.89% to 40.00%. Finally, statistical tests confirmed that our improvements were real and not random. This work provides a validated, practical model for enhancing quality and efficiency enhancements in knitwear manufacturing.