Abstract: Objective: To explore the expression of KAI1/CD82 and C-erbB-2 in breast cancer and its clinieal significance. Methods: The expression of KAI1/CD82,C-erbB-2 and estrogen receptor (ER) in 57 cases of breast cancer and 11 cases of benign mammary lesions were detected by immunohistochemistry S-P method,and their correlation with the clinicopathologic features was analyzed. Results: The positive rate of KAI1/CD82 was 31.58% in the breast cancer and 81.82% in the benign mammary lesions. The positive rate of C-erbB-2 was 71.93% in the breast cancer and zero in benign mammary lesions. The difference was statistically significant between the two groups (P < 0.01). The positive expression of KAI1/CD82 had statistical difference in cases with no metastasis of auxiliary lymph nodes and cases with negative expression of ER (P < 0.05). The positive expression of C-erbB-2 in cases with positive expression of ER was lower than that in cases with negative expression of ER (P < 0.05). The expression of KAI1/CD82 and C-erbB-2 in breast cancer had no correlation. Conclusions: KAI1/CD82 and C-erbB-2 both participate in the proceeding of breast cancer,they may help to evaluate the invasiveness and metastasis of breast cancer.