As all previous studies on ameliorative effects of garlic in renal damages have been done after diabetes induction, It was dedecided to assess its preventive roles on renal complications in rats with streptozotocin (STZ) -induced diabetes. Forty male wistar rats (250±20) were divided into 5 groups as follows: 1- Group normal (N) 2- Group Normal+Garlic (N+G), received garlic juice for 6 weeks.3- Diabetic (D) received STZ, 60 mg/kg BW /i.p.4- Group diabetic+garlic before (D+Gb), received garlic juice for 3 weeks before STZ injection and continued for more three weeks.5- Group diabetic+garlic after (D+Ga), three days after STZ injection, they received garlic juice for 3 weeks. Garlic juice was given by gavage (1ml /100g BW or (0.4 g/100gBW).Diabetes caused renal destruction (glomerular and proximal tubule hypertrophy, and atrophy of distal tubule epithelial cells). In addition, it leads to a decrease in renal weight. Garlic improved these changes so that the group receiving it before diabetes induction (D+Gb), showed more amelioration in variables than that receiving it after diabetes induction (D+Ga). In this study for the first time we showed that administration of garlic juice could play both preventive and therapeutic role on renal damage in diabetes.