Abstract: OBJECTIVE To explore the risk factors and preventive measures of nosocomial infection in elderly patients with breast cancer during the perioperative period. METHODS 328 cases of elderly breast cancer patients who underwent modified radical mastectomy from Jan.2012 to Sep.2017 were selected as the research objects.The infection rate of patients in the perioperative period was determined.Pathogens were isolated and cultivated from patients with nosocomial infection.Retrospective analysis of the clinical data of patients such as age, tumor location, tumor stage, pathological types, surgery duration and length of hospitalization was conducted.The independent risk factors affecting nosocomial infection were analyzed by univariate and multivariate logistic regression analysis. RESULTS In the 328 cases of breast cancer patients, there were 49 cases of nosocomial infection during the perioperative period, with an infection rate of 14.94%.Among the 49 cases of nosocomial infection, there were 20 cases of respiratory tract infection, 15 cases of incision infection, 6 cases of skin and soft tissue infection, 5 cases of urinary tract infection, and 3 cases of other infection.There were 61 strains of pathogens isolated from 49 cases of nosocomial infection, including 34 strains of gram-negative bacteria accounting for 55.74%, 21 strains of gram-positive bacteria accounting for 34.43%, and 6 strains of fungi accounting for 9.84%.The main gram-negative bacterium was Pseudomonas aeruginosa, the main gram-positive bacterium was Staphylococcus aureus.Multivariate logistic regression analysis results suggested age of ≥75 years old, operation duration of ≥100 min, length of hospital stay of ≥14 days, serum albumin level of ≥35 g/L, hemoglobin level of ≥70 g/L and combined chemoradiotherapy were independent risk factors for nosocomial infection (P＜0.05). CONCLUSION The incidence of nosocomial infection is higher in elderly patients with breast cancer during the perioperative period, dominated by respiratory tract infection and incision infection.Gram-negative bacteria are the main pathogens.Nosocomial infection is affected by many factors.Preventive measures should be taken to reduce the incidence of nosocomial infection.