Background Metabolic syndrome (MetS) and atrial fibrillation (AF) are causally related. This study aimed to determine the prevalence of MetS in patients with AF in the absence of structural heart disease from a tertiary hospital in China.Methods In a single center, 741 inpatients with AF in the absence of structural heart disease prior to catheter ablation were retrospectively reviewed. Among them, 588 (79.4%) patients had paroxysmal AF. Subgroup analyses were performed in paroxysmal AF and persistent/permanent AF.Results MetS was found in 343 (46.3%) patients (200 males, 143 females); 0, 1, 2, 3, 4, 5 components of the MetS were found in 59 (8.0%), 140 (18.9%), 199 (26.9%), 203 (27.4%), 103 (13.9%) and 37 (5.0%) patients, respectively. The prevalences of overweight/obesity, high blood pressure, high glucose level, high triglyceride level and low high density lipoproteins cholesterol level were 53.8%, 47.6%, 23.2%, 40.6% and 72.1%, respectively. The prevalence of MetS was not significantly different between the paroxysmal AF group and the persistent/permanent AF group (44.6% vs 52.9%,P=0.064). The five components of MetS except overweight/obesity (69.3% vs 49.8%, P <0.001) were not significantly different between the aforementioned two groups. The left atrium diameter increased with the sum of the MetS components. The left atrium diameter in the MetS group was significantly higher than that in the non-MetS group both in patients with paroxysmal AF and in patients with persistent/permanent AF.Conclusions The prevalence of MetS in patients with AF prior to catheter ablation is high. Further study and prevention are needed.