It was aimed to investigate the effects of grape seed extract (GSE) on structural changes that occur in renal tissues of rats with streptozocin (STZ)-induced diabetes. Rats were randomly divided into four groups (Control, Diabetes Mellitus (DM), GSE, Diabetes Mellitus+ GSE (DM + GSE) groups) each containing 8 rats. When GSE was given, the values of serum creatinine, BUN and uric acid in diabetics were decreased. Kidneys of diabetic group were found to have mild interstitial nephritis, tubular dilatation, hydropic degeneration, clotting necrosis in the tubular epithelium, dilatation in glomerulus and Bowman capsule, and hyperemia in glomerular capillaries. In the DM + GSE group, the glomeruli were normal, but hydropic degeneration was observed in some of the tubule epithelium. Only a few 8-OhDG positive cells were detected in tubule epithelium in the diabetes + grape seed group. The administration of GSE to diabetic patients helped to heal the deteriorated of kidney condition and DNA damage.