BACKGROUND AND OBJECTIVES: We aimed to investigate the relationship between the recurrence of atrial fibrillation (AF) and fibrosis marker soluble ST2 (sST2) in patients with nonvalvular paroxysmal AF (PAF). METHODS: We prospectively included 100 consecutive patients with PAF diagnosis and scheduled for cryoballoon catheter ablation for AF (47 males, 53 females; mean age 55.1±10.8 years). sST2 plasma levels were determined using the ASPECT-PLUS assay on ASPECT Reader device (Critical Diagnostics). The measurement range of these measurements was 12.5–250 ng/mL. Patients had regular follow-up visits with 12-lead electrocardiogram (ECG), medical history, and clinical evaluation. Twenty-four hours Holter ECG monitoring had been recorded 12 months after ablation. RESULTS: AF recurrence was detected in 22 patients after 1 year. Age, smoking history, diabetes mellitus,hypertension frequency, angiotensin converting enzyme inhibitor-angiotensin receptor blocker use, CHA2DS2VASc and HAS-BLED scores, serum sST2 level, left atrium (LA) end-diastolic diameter, LA volume and LA volume index were related to AF recurrence. In multivariable logistic regression analysis, sST2 was found to be only independent parameter for predicting AF recurrence (odds ratio, 1.085; p=0.001). Every 10-unit increase in sST2 was found to be associated with 2.103-fold increase in the risk of AF recurrence. The cut-off value of sST2 obtained by receiver operating characteristic curve analysis was 30.6 ng/mL for prediction of AF recurrence (sensitivity: 77.3%, specificity: 79.5%). The area under the curve was 0.831 (p < 0.001). CONCLUSIONS sST2, which is associated with atrial fibrosis, can be thought to be a useful marker for detection of patients with high-grade fibrosis who will get less benefit from cryoablation.