The purpose of this study was to investigate the effect of vitamin B2 deficiency on fuel metabolism in streptozotocin-induced diabetic rats. Thirty rats were fed a vitamin B2 deticient diet(-B2) or a control diet (＋B2) for 2 weeks and then subdivided into 3 groups respectively : base group, one day diabetic group and three day diabetic group. Diabetes of the rats were induced by streptozotocin injection into the tail vein. Glucose, glycogen, protein, alanine, triglyceride and free fatty acid were compared in plasma, liver, skeletal muscle of rats. Also, the total urinary nitrogen and glucose excertion were compared. Compared with ＋B2 rats, the increase of plasm glucose in -B2 rats due to the diabetes tended to be smaller. After diabetes were induced, the levels of plasma protein and alanine was significantly decreased and the urinary nitrogen excretion was significantly increased in -B2 rats. The level of plasma free fatty acid was increased continuously in B2 rats while increased at the first day and decreased at the third day diabetes was induced in ＋B2 rats. These results suggest that vitamin B2 deficiency increase protein catabolism due to the decrease of fatty acid oxidation. Thus, vitamin B2 deficiency in diabetes impair the adaptation of animals to the fuel metabolism and aggravate the body protein wasting which is one of the chronic complications of diabetes.