Abstract: Objective 　To investigate the expression of Smac and Ki67 in thyroid carcinoma and the corre2 lation of Smac and Ki67, the clinical significance as well. Methods 　Immunohistochemical staining of Smac and Ki67 expression was performed by the standard st reptavidin2peroxidase (SP) technique for the paraf2 fin sections of 87 thyroid carcinoma. The relationship between the Smac expression and the clincopatho2 logical parameters or Ki67 proliferation index was analyzed. Results 　The positive rate of Smac in thyroid carcinoma was 71. 3 %(62/ 87), all of the normal thyroid tissues expressed Smac (20/ 20) . Ki67 prolifera2 tion index in thyroid carcinoma was 42. 74 ±14. 52. Smac expression was significantly lower in patient s of male, over 45 years old, medullary and anaplastic thyroid carcinoma, stage Ⅱ, Ⅲand Ⅳ,and in those with invasions over cap sular ( P < 0. 05) . The Ki67 proliferation index in negative expression of Smac was sig2 nificantly higher than that in positive expression of Smac ( 40. 70 ±14. 68) vs (47. 78 ±13. 06 ), P <0. 05 . Conclusion 　Smac and Ki67 expression in thyroid carcinoma were significantly different f rom those in normal tissues, and they had significant correlation, which suggest that they may play an important role or even have synergic action in carcinogenesis and development of thyroid carcinoma.