Purpose: This study was to determine the effect of oral vitamin C supplements on blood sugar and antioxidative status in Types II diabetes mellitus patients. Method: Data for the study were collected from June 24 to August 31, 2001. Participants(31) took 1g/day vitamin C for 4 weeks, after a 1 - week taking no Vitamin C, followed by Vitamin C 3g/day for 4 weeks. A baseline blood sample was obtained following a 12hour overnight fast and at the end of each 4week Vitamin C administration. Blood samples were taken for plasma vitamin C concentration, fasting blood sugar, HbA1c, superoxide scavenging activity and hydrogen peroxide scavenging activity. The data were analyzed by SPSS for repeated measures ANOVA. Result: Plasma vitamin C concentration was significantly increased over dose(F=3.316, p=.043). Fasting blood sugar and HbA1c was significantly decreased over dose(F=13.192, p=.000; F=11.995, p=.000). Superoxide scavenging activity and hydrogen peroxide scavenging activity was significantly increased over dose(F=486.138, p=.000; F=177.704, p= .000). Conclusion: The results suggest that megadose vitamin C supplementation may have a beneficial effect in diabetes mellitus patients on both glycemic control and antioxidant status. Thus dietary measures to increase plasma vitamin C may be an important health strategy for reducing the compliance of diabetic patients