Objective To observe the effect of simvastatin on serum levels of matrix metalloproteinase-9(MMP-9) and tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) in patients with acute coronary syndromes (ACS).Methods 74 patients with coronary heart disease were studied.Among them,there were 34 patients with stable angina pectoris(SAP) and 40 patients with ACS.At the same time 25 cases of age matched healthy individuals were selected as a control.The serum level of MMP-gand TIMP-1 were compared among all groups.Results There was a significant difference in serum level of MMP-9and TIMP-1 among SAP group,ACS group and control group.The serum level of MMP-9 and TIMP-1 were different after treatment.Conclusion Plaque disruption may be related to the increased serum level of MMP-9 and the decreased serum level of TIMP-1 .Simvastatin can decrease serum level of MMP-9 and increase serum level of TIMP-1 in patients with ACS,and it may have a beneficial effect on clinical treating of patients with ACS.