Objective：To evaluate the effect of percutaneous coronary intervention（PCI） on mitral regurgitation （MR） in patients with acute myocardial infarction （AMI）. Methods, A total of 213 AMI patients were divided into PCI group（n = 87, PCI ＋ medication） and medication group（n= 126,medication） according to the treatments they received. Echocardiographic examination was conducted in patients during admission and 6 months follow-up. Color Doppler was used to determine the degree of MR. Echocardiogram indices included MR degree, left ventricular end-diastolic diameter （LVEDd）,left ventricular end-systolic diameter （LVEDs） ,left ventricular end-diastolic volume （LVEDV） ,left ventricular end-systolic volume（LVESV）, and left ventricular ejection fraction （LVEF）. Results： The overall incidence of MR was 28.6% in 213 patients during admission. The MR incidence in patients with acute inferior myocardial infarction was higher than that in patients with other parts of infarction （34.5 % vs 22.3 %, P〈0.01）. MR was found in 35.4 % patients during an average follow-up of 8.8 months. The MR incidence of PCI group was similar to that during admission（26.4% vs 27.6% ,P〈0.05）, while the incidence in medication group increased significantly than that during admission（43.7 % vs 30.2 %, P〈0.01）. Although the MR incidences were not significantly different between the 2 groups during admission, the incidence of medication group was significantly higher than that of PCI group during 8.8 months follow-up（P〈0.01）. LVEDd, LVEDV and LVESV in PCI group were smaller than those in medication group（P〈0.05） ,while LVEF in PCI group was higher than that in medication group（P〈0.05）. Conclusion： The MR incidence in patients with acute inferior myocardial infarction is higher than that in other patients. MR has an increasing trend as the time of myocardial infarction lasts. PCI can prevent MR through improving blood flow and left ventricular remodeling