Introduction: The isolation of superior vena cava (SVCI) and pulmonary vein isolation (PVI) improve the success rate of atrial fibrillation (AF) ablation. Limited information is available on the quantitative assessment of the narrowing of SVC after ablation. Methods: Ninety-one AF patients with SVC potentials were enrolled in this study. After PVI, SVCI was performed circumferentially at the level of the lower border of the right pulmonary artery. Radiofrequency (RF) pulses were delivered on a point-by-point basis for 30s at each point with an irrigated catheter in a temperature-controlled mode with the maximum temperature set at 42℃ and the maximum power at 25W. Follow up contrast-enhanced computed tomography was performed at four months after the ablation procedure. SVC narrowing was followed up in time (mean ± standard deviation = 20 ± 4.2 months). Results: All SVCIs were successfully achieved without severe complications. The pre-ablation SVC dimension at the level of the isolation line was 2.50 ± 0.94 cm2, and the post-ablation SVC dimension was 2.19 ± 0.82 cm2 (p = 0.016). Severe stenosis (reductions of SVC dimension > 75%) was not observed in this study. Moreover, the relationship between the SVC narrowing and the RF application time was not significant in this study. In the eight SVC cases with SVC narrowing, the mean SVC area recovered as a function time from 1.56 ± 0.42 cm2 to 1.80 ± 0.57cm2. Conclusion: The SVCI caused minor reductions in the SVC dimensions, but did not cause severe stenosis with life-threatening symptoms.