Background Despite radiofrequency catheter ablation (RFCA) of atrial fibrillation (AF) is known to be an effective treatment for rhythm control, pulmonary vein (PV) ostial ablation may increase incidence of PV stenosis. We evaluated pattern of PV stenosis in patients who underwent redo-RFCA of AF. Methods and Results In 8 patients (5 male, 55.2짹11.5 years old, 5 non-paroxysmal AF) with AF who underwent redo-RFCA, PVCT scans of baseline and immediate before redo-RFCA were evaluated and PV ostial diameters were compared by image-pro software. The interval between de novo RFCA and follow up PVCT was 505.5짹156.2 days and 4 of them underwent RFCA twice prior to the follow-up PVCT. PV ostial ablation was performed in 3 patients and antral ablation was done in 5 patients, respectively. Results: 1. The diameters of PV ostia reduced after RFCA (20.3짹5.5mm to 15.5짹5.8mm, p<0.01) and it was more prominent in left side PVs (left superior (LS) PV 23.0짹5.0mm to 16.4짹4.8mm, p<0.05; left inferior (LI) PV 17.6짹3.4mm to 12.1짹4.7mm, p<0.05). 2. The % reduction of left side PV ostial diameter was more significant in patients with repeated RFCA (-41.0짹21.3%) than those with prior single RFCA (-18.1짹14.2%, p<0.05). 3. There was no difference of % reduction of PV ostial diameter between circumferential ostial ablation and antral ablation (p=NS), and between 5mm tip ablation catheter and 8mm/irrigation tip catheter (p=NS). 4. The total number of RF energy delivery (R=0.24, p<0.01) and interval from1st RFCA to follow-up PVCT (R=0.22, p<0.01) had weak correlation with % reduction of PV ostial diameter. 5. Symptomatic significant PV stenosis was observed after PV ostial ablation in one patient and treated by a drug-eluting stent deployment (left inferior PV). Conclusion Both circumferential ostial ablation and antral ablation reduced PV ostial diameter, especially in left side PVs. Therefore, antral ablation at the more left atrial side is mandatory to prevent inadvertent complication of PV stenosis.