Abstract: Objective: To study the influence of neoadjuvant chemotherapy on tumor cell apoptosis and proliferation in patients with breast cancer.Methods: The apoptosis index(AI) of tumor cells in the neoadjuvant group and control group was assayed by TdT-mediated dUTP-biotin nick end labeling(TUNEL),and the Ki-67 antigen was examined by immunohistochemical method.Results: The AI of tumor cells was 9.26 in the neoadjuvant group and 3.36 in the control group.The difference was significant(P<0.01).The overexpression rate of Ki-67 antigen in the neoadjuvant group was 15.63,which was 50.0 lower than that in the control group(P<0.05). Conclusions: Neoadjuvant chemotherapy can induce tumor cell apoptosis and inhibit tumor cell proliferation in patients with breast cancer.