Abstract： Objective To explore the roles of nitric oxide(NO) and platelet activation abnormity in diabetic nephropathy(DN).Methods 74 type 2 diabetes mellitus(DM) patients were measured the levels of serum nitrites(NO - 2/NO - 3) a stable metabolic product of NO, and 62 among them were also determined the concentrations of GMP140(one of quota reflecting platelet activation) by ELISA. DM group were divided into three groups according to UAER(DM1: UAER <20ug/min, DM 2: UAER 20～200ug/min, DM3: UAER >200ug/min), and compared with 43 normal individuals(NC).Results Serum nitrites in DM1 were significantly higher than NC, but the NO levels of DM 2 and DM 3 were significantly lower than those; GMP140 in all of DM groups were higher than that in NC, espedaliy the DM 2 and DM3 were more increased than NC and DM1. NO in DM patients with hypertension were lower than that without hypertension, but GMP140 in DM patients with hypertension were higher than that without hypertension. There was significant negative correlation between NO and GMP140( r s=-0.52, P <0.05).Conclusion Elevated NO is related to renal hyperfiltration in early stage of DM. The decreased NO level in advanced DM may related to platelet activation, therefore promote the development of DN. The NO abnormity and the enbancement of platelet activation enhancement may be correlated with DN.