In perioperative chemotherapy for breast cancer, dexamethasone (DEX) is administered at high dose to prevent adverse effects. Abrupt cessation of high-dose DEX treatment induces fatigue, but the incidence of the fatigue is uncertain. In this study, we retrospectively evaluated the incidence of fatigue following DEX administration for supportive therapy and the improvement of fatigue with DEX tapering, a gradual reduction of the daily dose, in breast cancer patients. The subjects were 124 patients with breast cancer receiving epirubicin- or docetaxel-based regimens as perioperative chemotherapy. Of all patients, 16.1% of patients experienced fatigue after cessation of DEX administration. The severity of fatigue was grade 1 in 6.5% of patients, grade 2 in 8.1% of patients, and grade 3 in 1.6% of patients. There were no significant differences in dose and duration of DEX administration between the group with fatigue and the group without fatigue. In almost all patients with fatigue, DEX tapering was performed from the next cycle. The efficacy of DEX tapering was evaluated by comparing the grade and subjective symptoms. Following DEX tapering, the severity of fatigue was significantly reduced (p < 0.05), and the subjective symptom was improved in 94.7% of patients. Therefore, fatigue is occasionally induced after the cessation of DEX administration for supportive therapy in breast cancer patients. The tapering of DEX may be effective for fatigue.