Objective To investigate the clinical effect of 125I seeds implantation on bone metastasis from radioactive iodine-refractory differentiated thyroid carcinoma (RAIR-DTC).Methods A total of 9 RAIR-DTC patients with bone metastases (4 males,5 females,age range:42-87 years) between April 2014 and December 2016 were enrolled in this prospective study.Treatment plan was developed through treatment planning system (TPS).125I seeds implantation was performed under CT guidance.After 2 and 4 months,metastasis size,serum thyroglobulin (Tg) and verbal rating scale (VRS) pain score changes were recorded.Paired t test and two-sample t test were used for data analysis.Results VRS pain score decreased 2 months post-treatment comparing with that before treatment (2.56±0.88 vs 5.22±2.44;t =4.28,P＜0.01).VRS pain score at 4 months post-treatment was 1.78±0.83,which was lower than that at 2 months post-treatment (t =3.48,P＜0.01).The maximum tumor diameters before the implantation and 2 months post-treatment were (6.47± 1.84) cm and (5.08±2.11) cm,respectively (t =9.14,P＜0.01).The maximum tumor diameter at 4 months post-treatment showed a decreasing trend but it was not statistically different compared to that at 2 months post-treatment:((4.52±2.16) cm;t =2.19,P＞0.05).Serum Tg level reduced 2 months after the implantation (lgTg:2.71±0.85 vs 2.94±0.82;t =4.82,P＜0.01).Serum Tg level at 4 months post-treatment (lgTg:2.56±0.81) was lower than that at 2 months post-treatment (t =2.69,P＜0.05).Conclusions 125I seeds implantation is an effective method for treating bone metastasis from RAIR-DTC.It can help to shrink bone metastasis,alleviate pain and improve patients' quality of life.