Objective To assess the effect of 131I ablation of residual thyroid tissue in postoperative patients with differentiated thyroid cancer (DTC), and to investigate the influence factor for treatment effect. Methods 86 DTC patients with total or subtotal thyroidectomy generally underwent 1.85GBq～5.55GBq 131I treatment. The follow up was performed at 6 months after administration of 131I. Negative 131I scan, negative TgAb and Tg less than 5ng/ml were considered as treatment success. Results After 131I treatment, 50 patients (58.1%) were completely cured. 39 patients (69.6%) with total thyroidectomy were treated successfully. Conclusion 131I therapy is an effective and safe method for the treatment of postoperative patients with DTC. The volume of remnant thyroid is the important influence factor on the 131I ablation effect.