Background: Early statin therapy as the standard therapy for ACS patients is recommended by showing the clinical benefit through lipid reduction. Ezetimibe additional simvastatin showed primary cardiovascular preventing benefit in chronic renal disease. However, little is known about the efficacy and impact on clinical outcomes of ezetimibe/simvastatin in patients with acute myocardial infarction. Methods: We analyzed 1,465 patients who prescribed ezetimibe/simvastatin 10/20mg (n=395) or atorvastatin 40mg (n=1,070) at hospital discharge in Registry of Korean Patients with Acute Myocardial Infarction (KorMI). Serum levels of lipid profiles were followed up at 6 month. Clinical outcomes at 1 and 2 year defined as the major adverse cardiac event (MACE) were compared between atorvastatin and ezetimibe/simvastatin group. MACE were defined as the composite of death, MI, repeated percutaneous coronary intervention (PCI) and coronary artery bypass grafting .Results: Both group had significant reduction of low-density lipoprotein-cholesterol (LDL-C) at 6 month follow-up (-43.8% for ezetimibe/simvastatin 10/20mg, p<0.001; -40.9% for atorvastatin 40mg, p<0.001; inter-group p=0.077). The LDL-C lowering potency of ezetimibe/simvastatin was similar to atorvastatin. Patients who reached target value of LDL-C below 70 mg/dl between the groups were also comparable (86.0% vs. 85.8%, p=0.958). 1 year MACE was not different between the 2 groups (12.9% vs. 14.5%, p=0.323) with no difference in mortality, MI, and re-PCI rate. 2 year MACE was not also different between the 2 groups (32.9% vs. 32.4%, p=0.944) with no difference in mortality, MI, and re-PCI rate. Ezetimibe/simvastatin therapy was not inferior to atorvastatin therapy in the risk reduction of 1year (Hazard Ratio [HR] 0.80, 95% Confidence Interval [CI] 0.45-1.42) and 2 year MACE (HR 1.05, 95% CI 0.57-1.94) after adjustment. Conclusions: Ezetimibe/simvastatin therapy provided similar improvement of lipid profiles compared with atorvastatin therapy. Also ezetimibe/simvastatin 10/20mg therapy showed similar clinical outcomes compared with atorvastatin 40mg therapy. Ezetimibe/simvastatin 10/20mg therapy might substitute for high dose atorvastatin therapy, although further trials are needed.