Background: We assessed the temporal trends in risk factors, treatments, and clinical outcomes in Korea Acute Myocardial Infarction Registry (KAMIR1, KAMIR2, KorMI-Sub). Methods: 22,617 eligible patients (mean age 64.0짹13.2 years, male 70%) in Korea AMI Registry, from 2006 to 2009, were divided into 4 groups according to the admission date at 2006, 2007, 2008, and 2009 year. Risk factors, diagnosis of AMI, treatments, and clinical outcomes at hospital and 12-month were examined. Results: Between 2006 and 2009 year, mean age increased by 63.5 to 64.4 years. Male proportion between groups showed no significant change. There are increasing trends of hypertension (linear p=0.023), dyslipidemia (linear p<0.001), and family history of coronary artery disease (linear p<0.001), while decreasing trend of prior coronary artery disease (linear p=0.018). ST-segment elevation MI proportions decreased (linear p<0.001). Proportion of percutaneous coronary intervention (PCI) increased (linear p<0.001), while that of thrombolysis decreased (linear p<0.001). In patients who underwent PCI, symptom to door time increased (1013, 1044, 1259, and 1361 min, p<0.001), while door to balloon time decreased (1932, 1600, 1554, and 1273 min, p<0.001). The number of stents decreased (linear p<0.001). In patients who underwent thrombolysis, door to needle time increased (126, 154, 114, and 434 min, p<0.001). The kinds of thrombolytics did not show significant difference. In-hospital complications showed a decreasing trend (14, 14, 13, and 11%, linear p=0.001), while in-hospital deaths (5.1, 5.7, 5.5, and 5.8%, linear p>0.05) and 12-month major cardiac events (20, 23, 22, and 22%, linear p>0.05) did not show any increasing or decreasing trend. Conclusions: Between 2006 and 2009 year in Korea AMI Registry, there were significant trends regarding risk factors and treatments, but not clinical outcomes.