Background: An ECCOPG (Eastern China Cooperative Oncology Pharmacy Group) funded study was designed to compare the effect of 3 versus 6 mg pegfilgrastim for primary prevention of febrile neutropenia (FN) in Chinese breast cancer patients retrospectively. Methods: Patients undergoing a docetaxel and cyclophosphamide chemotherapy regimen, followed by pegfilgrastim, for primary prevention during 2018 and 2020 were retrospectively enrolled in the present study. The patients were divided into 2 groups according to the dose of pegfilgrastim. The incidence of severe neutropenia (absolute neutrophil count <0.5x10(9)/L), incidence of FN, and recovery time were calculated to compare the efficacy of different groups. P<0.05 was considered statistically significant. Results: A total of 295 patients were enrolled, 150 in the 3 mg pegfilgrastim group and 145 in the 6 mg pegfilgrastim group. No significant differences were found in the incidence of severe neutropenia (3 vs. 6 mg, 39.3% vs. 34.5%, P=0.401) and the incidence of FN (3 vs. 6 mg, 7.3% vs. 8.3%, P=0.830). Median recovery time was 2 days for both groups (P=0.485). Conclusions: 3 mg pegfilgrastim may be effective and safe for Chinese breast cancer patients as the primary prevention for FN. Prospective studies are needed to further confirm the prophylactic effect of 3 mg pegfilgrastim.