Aim To investigate the influence of high density lipoprotein(HDL) and oxidized high density lipoprotein(ox HDL) on secretion of nitric oxide(NO),nitric oxide synthase(NOS),and endothelin 1(ET 1) by ECV 304;To provide evidence for protection effect of HDL on endothelial cells. Methods Different concentrations of HDL and ox HDL were used to treat human umbilical endothelial cell line ECV 304. NO, NOS and ET 1 secreted by ECV 304 were detected with corresponding kits respectively. Results The results indicated that HDL increased NO and NOS secreting,and decreased ET 1 secreting.On the contrary,ox HDL decreased NO and NOS level,and increased ET 1 level in ECV 304. Conclusions HDL might protect endothelial cells and antiatherosclerosis by increasing NO and NOS secreting and decreasing endothelin 1 secreting,but after oxidized such effects were lost.