Abstract: AIM: To explore the effect of metabolic syndrome (MetS) on atrial fibrillation (AF) in coronary heart disease (CHD) patients. METHODS: A cross-sectional study was conducted in a cohort of 1805 hospitalized CHD patients who were divided into CHD+non-MetS group (n=1 150) and CHD+MetS group (n=655) according to MetS criteria. RESULTS: Incidence of AF in CHD+MetS group was higher than that in CHD+non-MetS group (14.2% vs. 8.1%, P<0.01). Left atrial diameter (LAD), left ventricular end-diastolic diameter (LVEDD), interventricular septum thickness (IVS), left ventricular posterior wall thickness (LVPW), left ventricular mass (LVM) and left ventricular mass index (LVMI) were higher in CHD+MetS group than those in CHD+non-MetS group (P<0.05), whereas left ventricular ejection fraction (LVEF) was lower (P<0.01). After adjustment for age, LAD and LVEDD, logistic regression analysis showed that MetS predicted the incidence of AF in CHD patients (OR: 1.631, P<0.05). AF patients (n=188) were more likely to be complicated with MetS than non-AF patients (n=1 617, 49.3% vs. 34.5%, P<0.01) with higher body mass index (BMI) and fasting plasma glucose (FPG)(P<0.05). Further logistic regression analysis suggested that obesity was the most closely related independent predisposing risk factor for AF (OR: 1.911, P<0.01). CONCLUSION: MetS is closely associated with the incidence of AF in CHD patients. Obesity is the most closely related predisposing factor for AF among all MetS factors.