Objective To explore the value of 18F-fluorodeoxyglucose (FDG) PET/CT for therapeutic assessment in patients with bone metastases from differentiated thyroid carcinoma (DTC) after 131I treatment.Methods Between January 2006 and August 2017,35 DTC patients (11 males,24 females,median age 60 years) with bone metastases who were treated with 131I and underwent 18F-FDG PET/CT scan were retrospectively analyzed.Therapeutic response assessment was based on morphological changes or the maximum standardized uptake value (SUVmax) changes of bone metastases,and the agreement (Cohen's Kappa coefficient) between two methods was analyzed.The progression-free survival (PFS) was estimated by Kaplan-Meier survival analysis and compared among patients with different treatment response (log-rank test).Results Morphological changes were consistent with SUVmax changes in 82.1％(23/28) of patients with positive 18F-FDG uptake (Kappa=0.731,95％ CI:0.628-0.834,P＜0.01).Five patients had stable disease according to morphological assessment,while 18F-FDG PET indicated they had metabolic response or disease progression.The serum thyroglobulin (Tg) levels confirmed the accuracy of 18F-FDG PET in 3 of those 5 patients.Compared with the patients with metabolically or morphologically progressive disease,patients who showed metabolically or morphologically stable disease or complete/partial response had significantly favorable prognosis (x2 values:4.132-6.543,all P＜0.05).Conclusions The therapeutic response based on metabolic criteria is in agree with that based on morphological criteria in most of the DTC patients with bone metastases.The SUV may act as a sensitive and efficient indicator of early therapeutic response or disease progression of bone metastases in DTC patients with positive 18F-FDG uptake.