Abstract： A 41-year-old male patient presented with generalized pruritic erythema and papules with occasional facial edema for one and a half years.The condition was absent in other members in his family.Peripheral blood film demonstrated an elevated count of morphologically normal eosinophils.Bone marrow biopsy revealed an increase in the proportion of eosinophils.Parasite eggs were undetected in stool samples by multiple examinations,and the blood sample was negative for antibodies against many parasites,antineutrophil cytoplasmic antibodies (ANCA),and FIP1L1/PDGFRα fusion gene.The level of blood myocardial enzyme was elevated.Colour Doppler ultrasound examination of the heart showed mild tricuspid incompetence,pulmonary valve incompetence and slight dilatation of the right atrium.The patient was diagnosed with complex undefined hypereosinophilic syndrome,which responded well to oral prednisone and intravenous cyclophosphamide.