In this study fifty 10 weeks old male albino rats weighing 150-200 g were used to investigate the effects of green tea extract on some physiological and histological parameters in alloxan induced diabetic rats. The animals were grouped as N.C, D.C, D.C+Insulin, D.C+GTE50 and D.C+GTE100 respectively. After treatments for four weeks, the results showed that the average body weight and the percentage of body weight gain of diabetic rats were significantly (P?0.05) reduced as compared with the rats of control group. WBC count, the levels of serum glucose, ALP, ALT, AST, creatinine, urea, uric acid, lipid profile cholesterol and triglycerides were significantly (P?0.05) increased in diabetic rats. Histological studies in pancreas, kidney, and liver showed structural changes. Administration of insulin and green tea extracts (GTE50, GTE100) for 28 days significantly (P?0.05) decreased the loss of body weight in diabetic treated rats. Significant decreases in the levels of physiological and hematological parameters were observed. Rats treated with GTE100 was found to almost restore the normal histological architecture of the pancreas, kidney, and liver of diabetic rats.