Background: Early statin therapy as the standard therapy for ACS patients is recommended by showing the clinical benefit through lipid reduction. However, little is known about the efficacy and impact on clinical outcomes among different kinds of statin in korean acute myocardial infarction patients. Methods: We analyzed 6,782 patients whose statin regimen was definite at hospital discharge in Korea Working Group on Myocardial Infarction (KorMI). Serum levels of lipid profiles were followed up at 6 month and compared between ezetimibe /simvastatin and atorvastatin (10mg, 20mg, 40mg). Results: Both ezetimibe/simvastatin group and atorvastatin group had significant reduction of low-density lipoprotein-cholesterol (LDL-C) at 6 month follow-up (ezetimibe/simvastatin: -30% for 10/10mg vs. -43.8% for 10/20mg, p<0.001; atorvastatin: -27.8% for 10mg vs. -36.7% for 20mg vs. -40.9% for 40mg, p<0.001; inter-group p=0.172). The LDL-C lowering potency of ezetimibe/simvastatin was similar to aotrvastatin. The greatest acquisition to target LDL-C value below 100 mg/ml was achieved in atorvastatin 40mg group (80.0% for 10mg vs. 84.5% vs. 85.8%, linear p=0.025) and ezetimibe/simvastatin 20mg group (77.3% for 10/10mg vs. 86.0% for 10/20mg, p=0.142). The greatest acquisition to target LDL-C value below 70 mg/ml was achieved in atorvastatin 40mg group (34.9% for 10mg vs. 43.8% vs. 51.4%, linear p<0.001) and ezetimibe/simvastatin 20mg group (39.4% for 10/10mg vs. 46.7% for 10/20mg, p=0.344). The acquisition of target LDL-C value below 100mg/dl and 70 mg/dl were comparable between atorvastatin 40mg group and ezetimibe/simvastatin 10/20mg group. Improvement of high-density lipoprotein-cholesterol, total cholesterol were similar between atorvastatin 40mg group and ezetimibe/simvastatin 10/20mg group. Conclusions: Ezetimibe/simvastatin therapy provided similar and non-inferior improvement of lipid profiles compared with atorvastatin therapy in Korean patients with AMI. Ezetimibe/simvastatin 10/20mg and atorvastatin 40mg were most effective doses in achieving target serum levels of LDL-C.