Background and Aim: Mesangial expansion may lead to renal failure due to the stenosis or occlusion of glomerular capillary lumen in diabetic patients. Oxidative stress is the main cause of diabetic mesangial expansion. The information obtained from the accurate estimation of mesangium volume, glomerular capillary volume and mesangial cells number via stereological methods is more reliable than that of morphometric or semi-quantitative variables in diabetic nephropathy investigations.Materials and Methods: Forty mature male rats were uninephrectomized and randomly divided into four groups as follows: group 1: the control group, group 2: diabetic without treatment, groups 3 and 4: diabetic treatment with SKEO 250 and 500 ppm in drinking water respectively. The treatment started after the induction of diabetes by alloxan. Treatment blood was sampled and the kidneys were fixed in formal saline solution after 8 weeks. Serum MDA was measured by thiobarbituric acid test. Kidney paraffin sections were prepared and stained via periodic acid Schiff (PAS) method. Mesangium volume, glomerular capillary volume and mesangial cells numbers were estimated via stereological methods. Data were analyzed via Mann Whitney U test at p<0.05.Results: Diabetes increased serum MDA, mesangium volume, mesangial cells number, and at once decreased glomerular capillary volume in comparison to control group. Treatment by SKEO ameliorated these variables when compared with group 2 (p<0.05).Conclusion: As an antioxidant agent, SKEO ameliorates diabetic mesangial expansion, glomerular capillary volume and mesangial cells numbers via inhibiting lipid peroxidation.