Objective: To investigate relationship between N-terminal pro-brain natriuretic peptide (NT-proBNP) level and new-onset atrial fibrillation (AF) in patients with acute myocardial infarction (AMI). Methods: A total of 236 AMI patients admitted within 24 hours of onset were tested for NT-proBNP level upon admission, and 1day, 3 days, and 7 days after primary percutaneous coronary intervention (PCI). All patients were monitored continuously for new-onset AF for 7 days, and were later divided into AF group (n=51) and non-AF group (n=185). Clinical manifestations, echocardiographic and angiographic data were also reviewed in all patients. The impact of NT-proBNP level on new-onset AF following initial AMI was analyzed with multi-factor Cox regression analysis.The receiver operator characteristic curve (ROC curve) was used to determine the predictive cutoff value of NT-proBNP for the occurrence of new-onset atrial fibrillation following initial AMI. Results: AF occurred in 21.6% of patients. The univariate analysis showed that patients with new-onset AF had an older age, larger left atrial diameter (LAD), higher C reactive protein （CRP）level,higher percentage of the population with high blood pressure, anterior AMI, left-anterior-descending-artery lesion and 3-vessel lesion, and lower left ventricular ejection fraction （P<0.05）. Levels of NT-proBNP were higher in patients with AF than those in patients without at any point of test (P<0.05). Area under ROC (AUC) of NT-proBNP to predict new-onset AF was 0.74（95%CI 0.60-0.90, P<0.01）, with an optimal cut-off value of 1 403.6 pg/mL. Multivariate analysis showed that NT-proBNP level (>1 403.6 pg/mL)(OR=1.8, 95%CI 1.3-2.4), age(>69 years old)（OR=1.6, 95%CI 1.3-3.1） and LAD(>43.8 mm) (OR=1.3, 95%CI为1.1-1.9) were independent predictors of occurrence of new-onset AF. Conclusion: Serum NT-proBNP level is of certain value in early prediction of the new-onset AF following AMI.