In early breast cancer chemotherapy, it is important to maintain the relative dose intensity(RDI). We retrospectively ana- lyzed the incidence and risk factors of febrile neutropenia(FN)among women receiving FEC(5-fluorouracil 500mg/m2, epirubicin 100mg/m2, and cyclophosphamide 500 mg/m2)chemotherapy. Of 72 patients, 33 patients developed FN and 39 patients did not. Excluding patients in whom the nadir could not be confirmed, we classified a final total of 28 patients into the FN group and 24 into the non-FN group. The number of leukocytes was significantly lower in the FN group(1,500/mL versus 2,146/mL, p=0.05). The reduction rate of leukocytes was also significantly lower in the FN group(74.5%versus 65.0%, p=0.02). In adjuvant FEC chemotherapy, the considerable reduction of leukocytes at nadir is a risk factor of FN. To manage FN appropriately, G-CSF therapy may be considered for these patients.