Abstract: Objective To study the expression of CD117 protein in breast invasive ductal carcinoma (IDC) and its relation with clinical pathological factors. Methods Expressions of CD117 protein, ER, PR, Her-2 in 40 primary breast IDC patients were detected with immunohistochemistry S-P method. Effect of IDC-related clinical pathological factors, including gender, age, TNM staging, histological grade and lymph node metastasis, on prognosis of IDC, were analyzed and assessed. Results The expression of CD117 protein was related with the histological grade, TNM staging and lymph node metastasis of breast IDC (P＜ 0.05), and increased with the histological grade of breast IDC and was positively correlated with the expressions of ER(r=5.28, P=0.03), PR(r= 4.67, P=0.04), HER-2(r=6.21, P=0.02). Conclusion Expression of CD117 protein may play an important role in the occurrence and development of breast IDC, and is one of the important indicators for the prognosis of IDC patients, thus providing a new target for the treatment of breast cancer.