PT. XYZ is an automotive component manufacturing company that produces Arm Rocker for two-wheeled and four-wheeled vehicles. This study aims to identify the type of defect, determine the main causes of defects, and provide improvement suggestions using the Lean Six Sigma method with the DMAIC approach (Define, Measure, Analyze, Improve, and Control). Data collection was carried out through observation, interviews, documentation, and company production data collection. At the Measure stage, DPU, DPO, DPMO, sigma levels, and Cpk values were calculated. Furthermore, at the Analyze stage, the root cause of the defect was identified using a fishbone diagram and the 5 Why Analysis method. The results showed that shaft hole scratch defects were influenced by chipped and burnt tool conditions, the direct drilling method, suboptimal coolant direction, and the absence of scratch inspection standards. Improvements were made through the application of the peck drilling method, coolant settings, periodic tool checks, spindle preventive maintenance, and improved lighting in the inspection area. After the implementation of the improvements, the number of defects decreased from 978 to 421 defects, the DPMO value decreased from 1,328.71 to 613.91, and the sigma level increased from 4.50 sigma to 4.73 sigma. These results indicate that the Lean Six Sigma DMAIC method is able to help reduce defects and improve the quality of the Arm Rocker production process at PT. XYZ