Aim To study the effect of oxidized low density lipoprotein(ox LDL) and antioxidant vitamin E (Vit E)on nitric oxide (NO) production and nitric oxide synthase(NOS) in cultured human umbilical vein endothelial cells (hUVEC). Methods The level of NO and NOS activity were measured by NO and NOS kits in hUVEC. Results ox LDL significantly decrease NO production from 126±24 mmol/g to 41±8 mmol/g and the activity of NOS in a dose and time dependent manners in hUVEC. Vit E can markedly increased ox LDL induced NO production and the activity of NOS in hUVEC. Conclusion ox LDL can markedly attenuate the NO synthesis, the possible mechanism of this effect was attributed to the decrease of NOS activity. Vita min E can elevated the production of NO via increasing the NOS activity. 还原