Backgound: Globally, breast cancer is the most frequently diagnosed malignancy and the leading cause of cancer death in women. Improvements in chemotherapy, surgery, lymph node evaluation and hormone receptor blocking therapy have successfully doubled the survival of breast cancer patients. Objective: To determine whether metformin use was associated with improvement in pathologic complete response (PCR) rate in patients with breast cancer receiving neoadjuvant chemotherapy. Patients and Methods: This prospective study was conducted at the Clinical Oncology Department, Aswan University and Upper Egypt Hospitals in the period between 1/7/2016 and 1/9/2019. This study included 50 patients divided into 2 groups, test group (metformin group) and standard group (non-metformin group). Histopathology was confirmed by tissue core biopsy. Results: All patients in the two groups in our study achieved either pathological complete response or partial response. No patients developed disease progression or were still stable disease. Among the patients in test group (metformin group), 15 patients (60%) achieved pathological complete response (PCR) while 10 (40%) patients did not achieve PCR. However, among the patients in standerd group (non-metformin group) 9 patients (36%) achieved pathological complete response (PCR) while 16 (64%) patients did not achieve PCR. There was statistically significant difference between the two groups regarding the response with better PCR in metformin group (p value is 0.089). Conclusion: The addition of metformin to neoadjuvant chemotherapy has a significant impact on pathological complete response (PCR) in female patients with advanced breast cancer.