Aim To study whether plasma very low density lipoprotein (VLDL), low density Lipoprotein (LDL), high density lipoprotein (HDL) were oxidatively modified in endogenous hypertriglyceridemia and effects of VLDL, LDL and HDL on blood coagulation and fibrinolysis in vitro. Methods Plasma VLDL, LDL and HDL were isolated with density gradient ultracentrifugation method. Human plasma triglycerides (TG), total cholesterol (TC),high density lipoprotein cholesterol (HDLC) were measured by enzyme method. The oxidative modification of LDL, VLDL and HDL was identified by agarose gel relative electrophoretic mobility (REM), absorbance at 234 nm and fluorescence of thiobarbituric acid reaction substances (TBARS). Prothrombin time (PT),activated partial thrombplastin time (APTT), plasminogen activator inhibitor 1 (PAI 1) activity and tissue plasminogen activator (t PA) activity were measured in the reaction system consisted of freshly mixed normal plasma according to the direction of the kits. Results The hypertriglyceridemia (HTG) group were 1.6 and 0.4 times more plasma TG, TBARS level than the control group respectively (P<0.01). The plasma HDLC in HTG group was 32% lower than that of the control group (P<0.01). The rela tive electrophoretic mobility, absorbance at 234 nm and TBARS of VLDL, LDL and HDL in HTG group were significantly higher than that of the control group (P<0.01). The PT and APTT of VLDL, LDL and HDL in HTG group were significantly shorter than that of the control group (P<0.05). The t PA and VLDL in HTG group was higher and the PAI 1 in VLDL in HTG group was lower than that of the control group (P<0.01), but LDL and HDL were not influenced by the t PA and the PAI 1 in HTG group and the control group. The correlation analysis indicated that electrophoretic mobility of VLDL and HDL in HTG group was negatively correlated with PT (P<0.01). Conclusions Oxidative modification of plasma very low density lipoprotein, low density Lipoprotein, high density lipoprotein occurred in endogenous hypertriglyceridemia in vivo. LDL and HDL enhanced the activity of blood clotting system in vitro, but only VLDL affected the activity of fibrinolysis system.