Objective To study the clinical value ofNa＋/I－ symporter (NIS) expression on thyroid carcinoma diagnosis and 131I therapeutic effects prediction. Methods Thirty-one cases of thyroid carcinomas enrolled in this hospital from 1998 to 2006 were included. Using immunohistochemical method, NIS expression location, positive cell staining and expression intensity were observed, which was calculated by immunohistochemical scores (IHS) and NIS expression level was compared between primary and metastatic carcinoma. Results NIS was over-expressed on the basolateral membrane in positive control——Grave disease tissue, and showed no staining in negative control. NIS was expressed in cytoplasm in all 31 primary carcinomas, and IHS was over or equaled to 4 in 80.65% of them. Except for 2 no staining, NIS was expressed in cytoplasm in the rest 28 metastatic carcinomas. NIS expression was related to the pathological type of thyroid carcinoma, the best in PTC, then FTC, and the weakest in fvPTC. NIS expression in metastatic carcinoma was related to that in primary carcinoma.Conclusion NIS is over-expressed in cytoplasm in most thyroid carcinoma, and the iodide uptaking defect is mainly due to its wrong location. It has great potential to be applied in clinic by that it can help with the differential diagnosis of benign and malignant thyroid diseases, especially between FTA and FTC, and that it can help predict the therapeutic effects of 131I therapy following thyroid operation.