Objective:To explore the expression of tumor metastasis suppressor KAI1 in membrane and cytoplasm of papillary thyroid cancer(PTC) cell; and to explore the clinicopathological significance of total expression of KAI1 protein in PTC. Methods:we used western blot to investigate:the KAI1 protein expression in membrane and cytoplasm in 30 primary PTC cases,13 cases of tissue near the cancer,7 cases of lymph node metastases and 13 benign cases ;total expressions of KAI1 protein in 30 PTC cases. Results:the expression of KAI1 protein in membrane was significant lower than that in cytoplasm of primary PTC;while the expression were unchanged in membrane and cytoplasm of tissues near the cancer,lymph node metastases and benign cases. The positive expression of KAI1 protein was correlated with the absence of lymph node metastases and the low stage of TNM;there were no significant correlation between KAI1 expression and primary tumor size or patient age. Conclusion:Loss of location in cell membrane may be the cause of KAI1 losing its ability to suppress the tumor progression and metastases. The low expression of KAI1 protein was significantly correlated with the clinical progression and lymph node metastases of PTC and it may be used to anticipate the progression and metastases,and may be the potential target of PTC for therapy.