The Sézary syndrome is a leukemic form of cutaneous T-cell lymphoma characterized by the presence of erythroderma covering at least 80% of the body-surface area, lymphadenopathy, and the presence of clonally related neoplastic T cells with cerebriform nuclei (Sézary cells) in the blood, skin, and lymph nodes. Hypereosinophilia can be caused by hematologic malignancy with clonal abnormality, which is often associated with Sézary syndrome. Sézary syndrome has rarely been reported in Korea. However, hypereosinophilia in the Sézary syndrome has not been reported in Korea. Here, we report a case of 75-year-old man with hypereosinophila, erythroderma, and cutaneous T-cell lymphoma which was finally diagnosed as Sézary syndrome.