Background: To explore the efficacy and safety of pegylated recombinant human granulocyte colony-stimulating factor (PEG-rhG-CSF, brand name: Jinyouli) in the prevention of neutropenia in breast cancer patients receiving adjuvant chemotherapy with EC regimen (epirubicin combined with cyclophosphamide). Methods: Retrospective analysis was conducted on breast cancer patients receiving adjuvant chemotherapy with EC regimen in Hengshui People's Hospital between January 2018 to October 2019. In cycle 1, all patients developed grade 3/4 neutropenia and PEG-rhG-CSF was used prophylactically in the subsequent cycles. The incidence of grade 3/4 neutropenia, febrile neutropenia (FN), chemotherapy delay and dose adjustment were observed as well as relative dose intensity (RDI), antibiotics application and adverse events. Results: 96 breast cancer patients were enrolled and all of them developed grade 3/4 neutropenia (100%) in cycle 1. After secondary prophylactic use of PEG-rhG-CSF, the incidence of grade 3/4 neutropenia decreased to 26.32% (25/95), 12.50% (10/80) and 13.63% (9/66) in cycle 2-4, respectively, with a statistically significant difference with cycle 1 (P<0.001); The incidence of FN decreased from 2.08% (2/96) in cycle 1 to 0% (0/95), 1.25% (1/80) and 0% (0/66) in the subsequent cycles (P>0.05). The incidence of chemotherapy delay was 2.08% (2/96), 2.50% (2/80) and 1.52% (1/66) in cycle 2-4, respectively, and the incidence of dose adjustment was 9.38% (9/96) in cycle 2. There was no dose adjustment in cycle 3-4. The average RDI was 92%, 92% and 94% in cycle 2-4, respectively. The most common treatment-related adverse events were fever (2.08%), muscle pain (1.04%) and fatigue (1.04%). Conclusions: PEG-rhG-CSF secondary prevention can effectively reduce the incidence of neutropenia in breast cancer patients receiving adjuvant chemotherapy with EC regimen, which ensures the implementation of standard-dose chemotherapy with good safety.