Abstract. From May to October 2025, the total volume of sweet potatoes collected reached 1,127,000 kg, with a defect rate of approximately 5%, indicating that the quality of the final product still requires improvement. The defects identified included rotten sweet potatoes, physical damage such as breakage and cracking, pest infestation, and sizes that did not meet established quality standards. During the observation period, the defect percentage fluctuated, with the highest levels recorded in June and July and the lowest in October. This study aimed to evaluate the product defect rate and determine the primary causes of defects in sweet potatoes by applying the Six Sigma method and Root Cause Analysis (RCA) to support quality improvement. The findings revealed that the defect rate at CV XYZ remains relatively high, with breakage identified as the most dominant type of defect, highlighting the need for continuous improvement efforts to enhance overall product quality.