Aim To investigate the effect of L-Aanginine and aminoguanidine on serum nitric oxide,nitric oxide synthase activity and renal function of diabetic rats. Methods Sixty healthy Wistar rats were involved in the study.The 24 hr urinary protein excretion(UPE),serum levels of nitric oxide(NO), total nitric oxide synthase(NOS) activity,inducible nitric oxide synthase activity and constructive nitric oxide synthase activity were detected to the rats.Streptozotocin(60 mg/kg) was administrated in the rats.The Streptozotocin(STZ) diabetic rats were randomly divided into diabetes control group,L-aanginine group and aminoguanidine group.At the end of 8 weeks after STZ administration,the above five indexes of the rats were detected and statistical analysis was carried out. Results Compared with normal rats: 24hUPE(43.92±7.38 mg),iNOS(19.75±3.85 kU/L) and NO(42.2±6.92 μmol/L) of the rats in diabetes(DM) control group increased significantly(p<0.01,p<0.05).In the rats of L-aanginine group,both 24hUPE(100.47±43.42 mg) and NO(67.34±18.87 μmol/L) increased significantly(p<0.01).In the rats of Aminoguanidine group,24hUPE(22.33±3.47 mg) increased while both tNOS(23.34±3.10 kU/L),iNOS(14.84±1.98 kU/L) and cNOS(8.50±2.25 kU/L) decreased(p<0.01,p<0.05).Compared with the diabetes control group,both 24hUPE and NO increased(p<0.05) in L-aang group at the end of 8 weeks.There was no obvious differences in tNOS,iNOS and cNOS levels in L-aanginine group,and the five indexes were significantly decreased in Aminoguanidine group(p<0.05).Compared with L-aang group,the five indexes were obviously decreased in Aminoguanidine group(p<0.05). Conclusion In early stage of diabetic nephropathy,administration of L-aanginine is harmful to the renal function while aminoguanidine is beneficial to the kidney via increasing or decreasing NO and NOS.