Abstract: Objective: To study the characteristics of arrhythmias in patients with acute ST segment elevation myocardial infarction（STEMI） and non-ST segment elevation myocardial infarction（NSTEMI）.Methods: Eligible patients were enrolled in the study, including 213 consecutive patients with STEMI and 159 consecutive patients with NSTEMI.Comparative analyses of various kinds of arrhythmias due to AMI were performed by cardiologists other than the ones who were involved in the study. （Results: The） rates of sinus bradycardias and ventricular tackycardias in patients with STEMI were significantly higher than those in NSTEMI, P=0.001,P=0.001,respectively.Howere,the rates of premature atrial complex and complete right bundle branch block（CRBBB） in patients with NSTEMI were markedly higher than those in STEMI,P=0.002,P=0.001,respectively.The rates of other arrhythmias developed due to AMI in the two groups were similar, P＞0.05.Conclusions: In the acute phase of AMI, malignant arrhythmias in STEMI patients are seen more frequently than in NSTEMI patients, which gives contribution to in-hospital mortality of the AMI patients. So, much importance should be attached to the arrhythmias developed in STEMI patients and corresponding treatments should be employed in time.