Introduction: Diabetes Mellitus is one of the main threats to human health in the 21^st century. Purpose: To evaluate the effect of vitamin C and/or vitamin E on liver, kidney and brain function of streptozoticin induced-diabetic rats. Study Design: One hundred and twenty male adult Sprague Dawley rats were divided into 6 groups (20 rats each), normal control, STZ-induced diabetic rat, STZ-induced diabetic rats treated with: antidiabetic drugs; vitamin C; vitamin E; vitamin C+E. Material and Methods: Blood samples were collected from all groups, Urea, creatinine, uric acid, total protein, Alanine/ aspartate transaminase and vitamin E were measured in plasma. Results: Urea, creatinine, uric acid, ALT, AST, vitamin E, LDH (in brain and liver) and MDA (brain) were significantly increased in STZ-induced diabetic rats. Treatment with vitamin C and/or E decrease significantly the increased level of the tested parameters and this may be due to the scavenging free radicals properties of vitamin C and/or E which prevents damage induced by hyperglycaemia; Also may be because vitamin C and/or vitamin E decreased lipid peroxidation and augmented the activities of antioxidant enzymes. Conclusion: Vitamin C and/or E may thus be a useful adjuvant therapy in the management of diabetes mellitus but it is better to use combination of the two vitamins rather than in single supplements to prevent the perturb antioxidant–proxidant balance.