A four-year-old female patient visited the pediatric hematologic clinic due to periodic generalized edema and eosinophilia. Laboratory assessment showed an eosinophil count of 40.02×109/L (73.6% of white blood cells). A bone marrow aspirate smear film showed no signs of malignant cells but had hypercellular marrow particles with eosinophilia (45% of all nucleated cells) and 52% of eosinophils were immature. Other laboratory tests showed an increased IgM level of 827 mg/dL, and lymphocyte phenotyping by flow cytometry revealed an aberrant CD3-CD4+ T-cell population of 27-53×109/L (1.9-3.6% of lymphocytes). Polymerase chain reaction analysis for the T-cell receptor gamma gene rearrangement showed a T-cell clonality peak. At the age of 13, allogeneic stem cell transplantation was performed, but with primary rejection. From the age of 17, she has continued receiving 3 mg/kg of reslizumab intravenously every 4 weeks for 21 months. Since reslizumab treatment was initiated, her eosinophil count remained consistently within the normal range. This is the first report describing the effective use of reslizumab in a Korean adolescent patient for the management of lymphocytic-variant hypereosinophilic syndrome (L-HES). Since the patient showed clinical manifestations of L-HES as well as episodic angioedema with eosinophilia (EAE), a continuous periodic examination is required given the higher risk of developing lymphoma or leukemia.