Aim To compare the differences of high density lipoprotein(HDL) antioxidant activity between normal people and the essential hypertension patients,and to explore the factors that may affect the antioxidant capacity of HDL. Methods Thirty-three patients with essential hypertension and 32 normal people were included.HDL and low density lipoprotein(LDL) were isolated by one-step density grandient ultracentrifugation,and induced oxidation with external Cu 2+.Antioxidant activity of HDL,lag time,lipid peroxidation degree were determined by spectrophotometric and thiobarbituric acid reactive substances methods.Paraoxonase 1(PON1) activity was measured with continuous monitoring using phenylacetate as substrate.Results In essential hypertension patients,the inhibitory effect of HDL on LDL oxidation and the activity of PON1 were reduced(p< 0.05),the lag time of oxidation and the lipid peroxidation degree did not show statistically significant difference.HDL antioxidant capacity was positively correlated with PON1 activity and negatively correlated with systolic pressure,diastolic pressure,and total cholesterol level(with r= 0.317,-0.387,-0.42,-0.259 respectively,p< 0.05).Conclusions HDL antioxidant activity may be one of the most important determinants for the development of atherosclerosis in patients with essential hypertension.The impaired HDL antioxidant activity is affected by high levels of blood pressure,and low activity of PON1.