Background: Neoadjuvant chemotherapy (NAC) in breast cancer patients provides an excellent model for evaluation of potential predictive factors. Both clinical complete response (cCR) and pathological complete response (pCR) achieved after neoadjuvant chemotherapy is a surrogate marker for a favorable prognosis. Factors capable of predicting response such as the proliferation marker Ki67 may help improve our understanding of the drug response and its effect on the prognosis and survival. Aim of the work: The aim of this study is to investigate the predictive value of the pretreatment Ki67 regard its ability to predict response to neoadjuvant chemotherapy and to investigate potential differences in proliferation scores between pretreatment core biopsies and post treatment final surgical samples in response to neoadjuvant chemotherapy. Patients & methods: A Retrospective Study conducted on sixty (60) eligible Female Patients with Non metastatic Breast Cancer patients receiving neoadjuvant chemotherapy. in the period from January 2015 till January 2020 at breast clinic unit at Ain-Shams University Hospitals Clinical Oncology department. All Patient characteristics, clinical and pathological data and immunohistochemistry analysis and treatment related data were thoroughly collected. Results: Pretreatment Ki-67 didn't show any significant difference with both clinical complete response (cCR) and pathological complete response (pCR) (all P > 0.05). A significant decrease in Ki-67 expression from a median 25% in core biopsy prior to therapy to 12 % in surgical specimen after NAC in non-pathological complete response (pCR) patients (P = 0.0006) Conclusion: Pretreatment K-i67 level Couldn't play a predictive role in predicting both clinical and pathological complete response. A significant change in Ki-67 expression was observed between core biopsy and surgical specimen after neoadjuvant chemotherapy in breast cancer patients