Background: Atrial fibrillation (AF) after coronary artery bypass grafting (CABG) is still the most common postoperative arrhythmic complication. Previous studies report that patients undergoing preoperative statin therapy had a lower incidence of postoperative AF. This study aimed to assess the effect of preoperative atorvastatin therapy on preventing AF following off-pump CABG in a randomized, controlled trial. Methods and Results: The 140 consecutive patients undergoing elective off-pump CABG, without a history of AF or previous statin treatment, were enrolled and randomly assigned to a statin (atorvastatin 20 mg/day, n=71) or a control group (placebo, n=69) starting 7 days preoperatively. The primary endpoint was the occurrence of postoperative AF; secondary endpoints were major adverse in-hospital cardiac and cerebrovascular events and identification of variables predicting postoperative AF. Atorvastatin significantly reduced the incidence of postoperative AF and the postoperative peak C-reactive protein (CRP) level vs placebo (14% vs 34%, P=0.009; 126.5 ±22.3 vs 145.2 ±31.6 mg/L, P<0.0001). Logistic regression analysis showed preoperative atorvastatin treatment was an independent factor associated with a significant reduction in postoperative AF (odds ratio (OR) 0.219, P=0.005), whereas a high postoperative CRP level was associated with increased risk (OR 2.011, P=0.013). Conclusions: Administration of atorvastatin 20 mg/day, initiated 1 week before elective off-pump CABG and continued in the postoperative period, significantly decreases postoperative AF. (Circ J 2009; 73: 2244-2249)