Background : Atrial fiblliration(AF) was related with poor prognosis in patient with acute myocardial infarction(AMI). A robust inflammatory response is an integral component of the response to tissue injury during acute myocardial infarction (AMI). Recent studies have implicated systemic inflammation in the genesis and maintenance of AF. However, the role of C-reactive protein (CRP) levels in the occurence of AF in patients with AMI has not been studied. This study investigated whether CRP is a risk factor for AF in patients with AMI in Korea. Method: We evaluated 9,164 patients underwent primary PCI with AMI in Korea AMI Registry (KAMIR), from Nov 2005 to Jan 2008. Blood samples and ECG were obtained at the time of admission to the hospital. CRP was measured by a high-sensitivity assay within 12 to 24 hours after symptom onset. All patients were evaluated by echocardiography to measure the left ventricular (LV) diameter and functions. Patients were categorized into 2 groups according to the presence of AF. Results : AF observed in 388 (4.2%) of all patients. There were no change of difference between the two groups in riak factors, cardiac enzyme elevation and LV systolic function The patients with AF were more observed in female(34.4% vs 20.1%, p = 0.024), advanced age (67짹12 vs 62짹12 years, p<0.001), had higher heart rate(86.2짹27 vs 77.4짹27 beats/min, p<0.001), larger LV end-systolic volume (70짹13 vs 65짹15, p=0.03) and higher hs-CRP level (2.62짹4 vs 1.96짹0.2, p=0.048). In multivariate analysis, only age (p = 0.03) and CRP levels (p = 0.04) were independent predictors of AF. Among the patients with AF, major adverse cardiac events were associated with LM disease (35% vs 7.3%, p=0.002), killip classification (I & II vs III & IV, p<0.001), old age (p=0.007). Conclusion : These results suggest that CRP may be a risk factor and killip classification was related with MACE for AF in patients with AMI.