Background: The COVID-19 pandemic seems to be ongoing in many countries, including Japan. ASCO and ESMO guidelines recommend treatment with during chemotherapy, and their use also reduces the risk of febrile neutropenia. On the other hand, there is a report that use of granulocyte colony-stimulating factor (G-CSF) increases the risk of admission and mortality due to COVID-19, so appropriate G-CSF use is still under discussion. Methods: Breast cancer patients treated with chemotherapy at our hospital from October 2020 to December 2022 were included in this study. We retrospectively collected patient data, including chemotherapy regimens, G-CSF use, COVID-19 infection, and COVID-19 severity, from electronic medical records. Results: Twenty-four patients (two bilateral breast cancers) received chemotherapy during this period. Twenty-three patients were female (95.8%) and one was male (4.2%), the mean age was 58.7 (34–79) years; 11 (45.8%) had early-stage breast cancer and 14 (58.3%) had advanced or recurrent breast cancer (one patient with early-stage breast cancer developed recurrent breast cancer during the study period). Seventeen cases (65.4%) were ER positive and nine cases (34.6%) were negative, 15 cases (57.7%) were PgR positive and 11 cases (42.3%) were negative, and six cases (23.1%) were HER2 positive and 20 cases (76.9%) were negative. The major chemotherapy regimens were ddAC in three patients (12.5%), AC in eight patients (33.3%), wPTX in 11 patients (45.8%), DTX in four patients (16.7%), TC in one patient (4.2%) and S-1 in eight patients (33.3%). Some patients also received treatment with anti-HER2 or anti-VEGF drugs or an immune check-point inhibitor but we did not consider these. Of the 13 patients who received AC, DTX and TC, 11 patients received PEG-GCSF in all their cycles. Among all patients receiving, COVID-19 symptoms were suspected on four occasions, and the COVID-19 antigen test was conducted, but all were negative, so no cases of COVID-19 were observed. Of the 46 cycles of AC, DTX, and TC, the proportion of patients with suspected COVID-19 symptoms who underwent antigen testing tended to be lower in the PEG-GCSF group (37 cycles) than in the no PEG-GCSF group (nine cycles) (2.7% vs. 22.2%; p = 0.0933, Fisher’s exact test). Conclusions: In this study, we did not find any cases of COVID-19 infection during chemotherapy, and so were unable to analyze the association between G-CSF use and COVID-19 infection severity. However, we did observe a trend toward a lower rate of potential COVID-19 with administration of PEG-GCSF. This might reflect a better quality of life for breast cancer chemotherapy patients.