Abstract Background Left atrial low-voltage areas (LVAs) were known to be associated with atrial fibrosis and atrial fibrillation (AF) recurrence after catheter ablation. However, the association between body mass index (BMI) and prevalence of LVAs has not been fully elucidated. We hypothesized that LVAs were more frequently found in patients with abnormal BMI than in those with normal BMI. Purpose The purpose of this study was to clarify the association between body mass index (BMI) and the prevalence of LVAs in patients with AF ablation. Methods Between December 2014 and March 2022, 1,479 (age, 68±10 years; female, 500 [34%]) consecutive patients who underwent initial AF ablation were enrolled. BMI was divided into four groups, namely <18.5 kg/m², 18.5-25 kg/m², 25-30 kg/m², ≥30 kg/m². LVAs was defined as areas with bipolar voltage of <0.5 mV covered ≥5 cm² of left atrium. Rhythm outcome following the catheter ablation procedure was also followed for 24 months. Results LVAs were found in 349 (24%) patients. J-curved phenomenon existed between BMI and the prevalence of LVAs (Figure 1). In particular, BMI <18.5 kg/m² was an independent predictor of LVAs on multivariate analysis (odds ratio, 1.9; 95% confidence interval: 1.01–3.5; p=0.046). As for rhythm outcome, there was significant difference in freedom from AF recurrence among groups stratified by BMI (Figure 2). Conclusions Between BMI and the prevalence of LVAs, J-curved phenomenon existed in patients with AF ablation. There was significant difference in rhythm outcome following AF ablation among groups stratified by BMI.Figure 1Figure 2