The proliferation of arterial SMC plays an important role in process of atherosclerosis. Oxidized HDL(OX-HDL) can increase ³H-TdR incorporation to DNA of cultured human arterial SMC, so promote proliferation of SMC. A study on effect of OX-HDL on proliferation of cultured human arterial SMC with MTT method was made. It was showed that native HDL(N-HDL) has no effect on proliferation of SMC but OX-HDL significantly stimulated the proliferation of SMC (P＜0.01);N-HDL significantly inhibited proliferation of human SMC induced by OX-LDL (P＜0.01) and OX-HDL significantly enhanced proliferation of human SMC induced by OX-LDL (P＜0.01).