Background The association between alcohol consumption, atrial substrate, and outcomes after atrial fibrillation (AF) ablation remains controversial. This study evaluated the impacts of drinking on left atrial substrate and AF recurrence after ablation. Methods and Results We prospectively enrolled 110 patients with AF without structural heart disease (64±12 years) from 2 institutions. High-density left atrial electroanatomic mapping was performed using a high-density grid multipolar catheter. We investigated the impact of alcohol consumption on left atrial voltage, left atrial conduction velocity, and AF ablation outcome. Patients were classified as abstainers (<1 drink/wk), mild drinkers (1-7 drinks/wk), or moderate-heavy drinkers (>7 drinks/wk). High-density mapping (mean 2287±600 points/patient) was performed on 49 abstainers, 27 mild drinkers, and 34 moderate-heavy drinkers. Low-voltage zone and slow-conduction zone were identified in 39 (35%) and 54 (49%) patients, respectively. There was no significant difference in the proportions of low-voltage zone and slow-conduction zone among the 3 groups. The success rate after a single ablation was significantly lower in drinkers than in abstainers (79.3% versus 95.9% at 12 months; mean follow-up, 18±8 months; =0.013). The success rate after a single or multiple ablations was not significantly different among abstainers and drinkers. In multivariate analysis, alcohol consumption (=0.02) and the presence of a low-voltage zone (=0.032) and slow-conduction zone (=0.02) were associated with AF recurrence after a single ablation, while low-voltage zone (=0.023) and slow-conduction zone (=0.024) were associated with AF recurrence after a single or multiple ablations. Conclusions Alcohol consumption was associated with AF recurrence after a single ablation but not changes in atrial substrate.