A 36-year-old woman was admitted to our hospital after modified radical mastectomy operation. Adjuvant chemotherapy was administered using TAC regimen. Severe neutropenia occurred after chemotherapy. Granulocyte colony stimulating factor (G-CSF) was given to treat neutropenia. On the second day of G-CSF use, the patient complained of swelling of her neck on the left side, which subsided spontaneously after discontinuation of G-CSF medication. However, the same symptom recurred following G-CSF use on the second cycle of chemotherapy. B-mode ultrasound showed swollen lymph nodes and biopsy revealed no evidence of metastasis. Therefore, the unilateral lymphadenopathy is considered to be the side effect of G-CSF, which is very rare.