Evaluation of body composition and sarcopenia status could provide evidence for more sensitive prediction of chemotherapy toxicities and support mitigation of the negative impacts of chemotherapy. This study evaluated associations among hematologic toxicities, sarcopenia, and body composition change in breast cancer patients undergoing neoadjuvant chemotherapy.This retrospective cohort study employed data from 298 breast cancer patients undergoing neoadjuvant chemotherapy. We evaluated two abdominal computed tomography scans before and after neoadjuvant chemotherapy to identify body composition change. As hematologic toxicities, severe (grade 3 or 4) anemia, neutropenia, and thrombocytopenia were assessed throughout the treatment period using Common Terminology Criteria for Adverse Events (version 5.0).Participants experienced severe neutropenia (23.5%), anemia (7.1%), and thrombocytopenia (0.7%) during chemotherapy. After chemotherapy, the group with sarcopenia had double the anemia prevalence of the group without sarcopenia (p < 0.001). The group with anemia had significantly decreased skeletal muscle index (SMI, p = .0013) and subcutaneous fat index (SFI, p = .0008). Almost 50% of the sarcopenia group treated with an AC-T (weekly) regimen (combined anthracycline and cyclophosphamide followed by a weekly taxane) had neutropenia. Multiple logistic regression showed that the AC-T (weekly) group had higher neutropenia prevalence than other regimen groups.Our findings of higher anemia prevalence in breast cancer patients with sarcopenia and decreased SMI and SFI after neoadjuvant chemotherapy provide evidence of a relationship between anemia and body composition change. Early screening and combined consideration of body composition change, sarcopenia status, and chemotherapy regimen could improve clinical outcomes.