This study aims to minimize the defect rate in the sewing section of a garment industry in Bangladesh using the Lean Six Sigma DMAIC methodology. The industry faces some of the major issues such as production imbalances, poor line efficiency, low productivity and high defect rates, as a result of these issues cause manufacturers to suffer losses, thereby harming the profitability and global competitiveness of the RMG industry in Bangladesh. To eliminate these inconveniences, this paper applies the DMAIC Methodology to identify, analyze and reduce defects in a sewing section of a Bangladesh garment industry. In order to deal with these problems systematically a data-driven DMAIC methodology was used to identify analyze and reduce defects in the sewing section. Following the use of DMAIC approach, the defects rate decreased from 15.52% to 14.93% and the sigma level raised from 2.51 to 2.54, indicating a statistically significant defect reduction confirmed by hypothesis testing. The garment industry should utilize the six sigma DMAIC methodology significantly to improve operational performance, enhance quality assurance systems and build a culture of continuous improvement significantly.