Abstract: Objective To study the role of ER K1/2(extracellular signal-regulated kinase 1 and 2,ER K1/2 or p42- 44MARK)signal pathway in proliferation of vascular smooth muscle cells induced by oxidized low density lipoprotein.Methods Two-factorial experiment was designed to explore the influence of four dosage levels of Ox-LDL(0,50,100,200 μg/ml)at three different stagesof exposure(24,48 and 72hr)onproliferation of arotic vascular smooth muscle cellsof rabbit.Activities of ERK1/2 in the cultural vascular smooth muscle cells were observed with different epxosure level of Ox-LDL at different time.Special inhibitor(U0126)of ERK1/2 was used to investigate the role of ER K1/2 in proliferation of the aortic VSMCs induced by Ox-LDL.Results The proliferation of VSMCs was higher than that of control group when the cell treated with Ox-LDL at levels of 50,100μg/ml.But the proliferation of VSMCs induced by Ox-LDL was seriously reduced at 200μg/ml.The activity of ERK1/2 was also changed after the cells were treated by Ox-LDL.Special inhibitor(U0126) could inhibit cell proliferation induced by Ox-LDL.Conclusion Ox-LDL induced the proliferation of VSMCs,which were associated with the dose and time of expousre.The signal pathway of ER K1/2 may play the key role in the proliferation of VSMCs induced by Ox-LDL.