Abstract: OBJECTIVE To investigate the types of postoperative infection in the breast cancer patients undergoing chemotherapy and analyze the species of pathgeons. METHODS A total of 294 breast cancer patients who were treated in the hospital from Jan 2014 to Jan 2018 were recruited as the study objects, the infection sites of the patients with postoperative infection were statistically analyzed, the clinical data were collected, the related factors for the postoperative infection were analyzed, the blood specimens that were collected from the patients with postoperative infection were cultured, and the species of pathogens were statistically analyzed. RESULTS Totally 58 patients had postoperative infection, with the incidence rate 19.73%; the incidence rate of respiratory tract infection was the highest, totally 30 patients had the respiratory tract infection, accounting for 51.72%. The myelosuppression, drainage duration more than 10 days and blood transfusion (unfiltered white blood cells) were the related factors for the postoperative infection in the breast cancer patients, and there were significant differences (P＜0.05). The myelosuppression and drainage duration were the independent risk factors for the postoperative infection in the breast cancer patients undergoing chemotherapy (P＜0.05). Totally 46 strains of pathogens were isolated from the 58 breast cancer patients with postoperative infection, 27 (58.70%) of which were gram-negative bacteria, and 16 (34.78%) were gram-positive bacteria. The drug resistance rate of the 15 strains of Escherichia coli was 86.67%, the drug resistance rate of the 9 strains of Klebsiella pneumoniae was 88.89%, and the drug resistance rate of the 11 strains of Staphylococcus aureus was 100.00%. CONCLUSION The incidence rate of postoperative infection is high in the breast cancer patients undergoing chemotherapy, the patients with respiratory tract infection are dominant. It is necessary for the hospital to attach great importance to the myelosuppression, drainage duration and blood transfusion so as to reduce the incidence of the postoperative infection. The gram-negative bacteria are dominant among the pathogens causing the postoperative infection in the breast cancer patients.