Abstract： Objective To investigate the critical value of TSH-stimulated Tg(sTg) in the diagnosis of metastasis from DTC,and to evaluate the diagnostic value of the ratio of sTg to suppressed Tg (sTg/suppressed Tg).Methods A total of 330 post-operative DTC patients(87 males,243 females,age range:12-70 years)who underwent thyroid remnant ablation from August 2008 to December 2014 were retrospectively reviewed.Their serum TgAb levels were normal.The patients were divided into non-metastasis group (147 cases) and metastasis group(183 cases) according to results of ultrasonography,CT and WBS.The difference of sTg between the two groups were compared by Mann-Whitney rank sum test.ROC curve was used to analyze the relationship between sTg,sTg/suppressed Tg ratio and metastasis,the cutoff value was calculated.Results The sTg was significantly different between the non-metastasis group and metastasis group:1.0 (0.1,2.0) μg/L vs 36.5 (3.9,126.7) μg/L;u=-6.642,P＜0.05.The AUC for ROC curve in metastasis group was 0.85,and the cutoff value was 2.05 μg/L,with the sensitivity 85.2％,specificity 67.3％,and accuracy 82.3％.While sTg＜2.05 μg/L,the AUC of sTg/suppressed Tg ratio was 0.941,and the cutoff value was 4.3,with the sensitivity 93.3％,specificity 88.2％,and accuracy 92.3％.Conclusions The sTg has a specific value for the diagnosis of metastasis from DTC after operation and the cutoff value is 2.05 μg/L in this set of patients.The ratio of sTg/suppressed Tg could be used to correct the sTg and to improve the diagnostic sensitivity.