Abstract: The aim of the present study was to compare the effects of the elaidic acid( 9t18 ∶ 1) and the trans-Vaccenic acid( 11t18 ∶ 1) on endothelial cells injury. After adding different concentrations of 9t18 ∶ 1 11t18 ∶ 1,the cell viability,cell morphology,oxidase activity( SOD and MDA),LDH leakage rates,effects of NO content and NOs activity were obserred.The results showed that 9t18∶1 and 11t18∶1 reduced the cell survival rate,and the inhibitory effect of 9t18∶ 1 on proliferation of endothelial cells were stronger than 11t18 ∶ 1 in 100 μ mol / L.Both of trans fatty acids lead to changes in endothelial cell morphology,cells from normal spindle to round and edge became rough.9t18∶1 and 11t18 ∶ 1 increased LDH leakage rate and MDA in endothelial cell,but the 11t18 ∶ 1- treated group was reduced than 9t18∶1 in the same concentration.NO secretion,NOS and SOD activity was reduced by 9t18∶1 and 11t18∶1,but 11t18∶1 group was significantly higher in the same concentration of 9t18 ∶ 1. Both of 9t18 ∶ 1 and 11t18 ∶ 1 could increase the mRNA expression levels of ICAM,VCAM,and IL-6,the former was obviously higher than the latter.In summary,the HUVEC cells injury induced by 11t18∶1 was significantly weaker than that of 9t18∶1.