Abstract: 115 patients of postoperative thyroid cancer are treated with 131I to ablate for residual normal thyroid tissue. 2 960~3 700 MBq (80~100 mCi) 131I ablative dose is administrated. 80-120 mg thyroid extract is given for 3 months, then stopped. 50μg T3 daily is given for 15 days and stopped for over 15 days. The 131I whole-body scan are performed. The effective rate of 131I ablation is 70%.