Background: Renal dysfunction is associated with a higher rate of atrial fibrillation in clinical practice. This study investigated the associations between renal function, left ventricular (LV) diastolic dysfunction, and postoperative atrial fibrillation (POAF). Methods and Results: A total of 265 consecutive patients who underwent cardiac surgery were prospectively enrolled in the study. Echocardiography was performed before cardiac surgery. The patients were divided into 3 groups based on estimated glomerular filtration rate (eGFR) (group 1, ≥90ml·min-1·1.73m-2; group 2, 60-90ml·min-1·1.73m-2; and group 3, <60ml·min-1·1.73m-2). POAF occurred in 83 of 265 patients (31.3%). The rate of new-onset POAF increased from 15.2% (12/79) in group 1 to 27.8% (27/97) in group 2 and 49.4% (44/89) in group 3 (P<0.001). Further, with increasing renal dysfunction from groups 1 to 3, the rate of LV diastolic dysfunction - defined as E/e' >15 - also increased (group 1, 19.0%; group 2, 38.1%; and group 3, 48.3%; P<0.001). Absolute eGFR was significantly correlated with E/e' ratio (r=-0.39, P<0.001). Renal function remained as the independent predictor of POAF on multivariate analysis (odds ratio, 1.90; 95% confidence interval: 1.26-2.87; P=0.002). Conclusions: In patients undergoing cardiac surgery, decreased eGFR was associated with an increased rate of LV diastolic dysfunction with a subsequent increase in the rate of POAF.