Abstract: Objective To study the relationship between the expression of nm23-H1、p16 protein and thyroid carcinomas Method Immunohistochemistry was used to detect the expression of nu23-H1、p16 protein in 54 thyroid carcinomas、16 thyroid adenomas、9 nonneoplastic thyroid tissues and 12 adjacent normal tissues Results The expression of nm23-H1 and p16 was much higher in thyroid adenomas and differentiated carcinomas (P＜0.05),whereas it was much lower in undifferentiated carcinomas (P＜0.01).Positive correlation was observed between the expression of nm23-H1、p16 protein and the degree of differentiation(P＜0.01).There was no significant association betwen the expression of nm23-H1、p16 protein and the cervical lymph node metastasis,but the expression of nm23-H1 was negatively corrated with capsule invasion(P＜0.05). Conclusion The loss of nm23-H1 and p16 function may play an important role in carcinogenesis and progress of thyroid undifferentiated carcinoma.Although the expression of nm23-H1 and p16 can't be used as a marker of low metastatic potential,it may serve as a good marker for the degree of differentiation and biological behavior.