The purpose of this study was to investigate the effects of purple-fleshed potatoes on blood glucose level (BGL), insulin and lipid levels in streptozotocin (STZ) induced diabetic rats for 7 weeks. Test groups were divided into non-diabetic control and diabetic groups. The diabetic groups were further divided into three groups: diabetes mellitus (DM) control, 10% purple-fleshed potato DM (10PP-DM), and 20% purple-fleshed potato DM (20PP-DM) groups. Three weeks after initiating the experimental diet, BGL was significantly lower in the 10PP-DM and 20PP-DM groups compared to the DM control group. As for serum insulin levels, the 20PP-DM group was significantly higher than in the DM control group. While serum cholesterol level was significantly lower in the 20PP-DM group, serum triglyceride level was significantly lower in the 10PP-DM group than in the DM control group. We concluded that a 20PP powder intake improves both diabetes and lipid control in diabetic rats by significantly improving serum insulin level and lowering BGL and serum cholesterol level.