Objectives: The present study was carried out to investigate the preventive effects of Samgijiwhang-Tang(SJT) on streptozotocin(STZ)-induced diabetic nephropathy. Methods: SIT was given to rats through oral administration. The experimental animals were divided into a normal group of rats, a control group of STZ-induced diabetic rats, and a sample group with SIT administration. Rehmanniae Radix Preparat is combined in the original prescription of SIT, but in this experiment, Rehmanniae Radix was combined instead of Rehmanniae Radix Preparat to compare the effects of anti-diabetic nephropathy. Experimental diabetic nephropathy was induced by the injection of STZ(60mg/kg) in the rat via the peritoneum. The effect of SIT on STZ-induced diabetic nephropathy was observed by measuring the serum level of creatinine and BUN, in addition to urine secretion of albumin for 24 hours and the level of glucose found in the urine. Anti-oxidative stress of SIT administration in a living body was estimated by measuring lipid peroxide and GSH content in the cortex of kidneys. Results: STZ induced an increase of serum creatinine, urine glucose and renal cortical lipid peroxidation was lowered by Rehmanniae Radix Preparat combined SIT administration. Conclusions: The SIT treatment showed a protective effect on the rat diabetic nephropathy model, and action mechanism of the effect was thought to be concerned with anti-oxidative stress.