Obesity is a well-known risk factor for various cardiovascular diseases. Recent clinical data showed that overweight and obese patients have higher incidence of atrial fibrillation (AF) compared with individuals with normal body weights, but the underlying mechanisms remain to be elucidated. In this study, we investigated the effects of a high fat diet on atrial activities in mice. ICR male mice were fed a regular diet (RD) or a high fat diet (HFD) for 8 weeks. Mice fed HFD showed significantly greater body weight gains and visceral fat accumulation compared with RD mice. Under anesthetic condition, baseline arterial blood pressure and heart rate were not significantly different between RD and HFD groups. Although no spontaneous or atrial stimulation-induced atrial fibrillation was observed, this study revealed several alterations in the activities and protein levels in the atria in HFD mice. Surface electrocardiogram (ECG) revealed significantly shortened PR interval in HFD mice. In the atrial stimulation experiments, the sinoatrial (SA) node recovery time was significantly prolonged whereas the atrial effective refractory period was significantly reduced in HFD mice as compared with RD mice. Western blot showed protein levels of two major potassium channels, Kv1. 5 and Kv4. 2/3, were significantly increased in atria of HFD mice. These data indicate that HFD induces atrial electrophysiological remodeling in mice, which may be a potential mechanism underlying the increased risk for atrial arrhythmias in obesity and metabolic disorders.