The aim of this study was to evaluate whether the levels of HbA1c could predict the outcome of ablation in patients with type 2 diabetes mellitus (T2DM) and paroxysmal atrial fibrillation (PAF). The study comprised 149 consecutive patients with T2DM and PAF who underwent their first circumferential pulmonary vein isolation. HbA1c levels were measured before ablation. Cox proportional hazards models were constructed to assess the relationship between HbA1c levels and the recurrence of atrial fibrillation (AF). Of the 149 patients, 60 (40.3 %) developed AF recurrence after a median 12-month follow-up. Multivariate Cox regression analysis revealed that left atrium size and HbA1c were independent predictors of recurrent atrial tachyarrhythmia. Receiver operating characteristic analysis demonstrated that an HbA1c cut-off value of a parts per thousand yenaEuro parts per thousand 6.9 % predicted recurrence with 55.0 % sensitivity and 67.4 % specificity (AUC = 0.634). The success rate of ablation was 69.0 % in patients with an HbA1c value of < 6.9 % compared with 46.8 % in those with an HbA1c value of a parts per thousand yenaEuro parts per thousand 6.9 % (log-rank test, p = 0.004). High levels of HbA1c were associated with an increased risk of recurrence of atrial tachyarrhythmia in patients with T2DM and PAF undergoing catheter ablation.