Objective: To investigate effects of Nigella sativa or black cumin oil (BC) on renal pathophysiology in streptozotocin-induced diabetic rats. Methods: Male Sprague-Dawley rats were carried out and divided into four groups: control rats given tap water (CON) or administered with BC (CON-BC), diabetic rats given tap water only (STZ) or administered with BC (STZ-BC). Diabetes mellitus was induced by an injection of streptozotocin in the rats. BC (1000 mg/kg) was orally administered for 8 weeks. Renal functions and pathology were studied. Results: As comparing with STZ rats, renal hemodynamics of STZ-BC rats showed the significant increases in glomerular filtration rate, effective renal plasma flow and effective renal blood flow, while renal vascular resistance and filtration fraction were decreased. The improvement of tubular dysfunction in STZ-BC rats were indicated by the significant decreases in fractional excretion of water and Mg++ . A decrease in number of abnormal glomeruli was apparent in the diabetic rats administered with black cumin. Conclusion: BC administration could restore renal dysfunction and attenuate glomerular pathology in the streptozotocin-induced diabetic rats. The mechanism may involve in vascular function. The effect of Nigella sativa on the inhibition of rennin-angiotensin system and mesangial matrix production in diabetic rats is interesting for a further study.