The idiopathic hypereosinophilic syndrome (HES) is a disorder marked by the sustained overproduction of eosinophils. The disease is characterized by damage of multiple organ including heart, nerve system, skin and lung due to eosinophilic infiltration and the diagnosis is one of exclusion. Rheumatologic manifestations of HES are infrequent. In about 10~40% of rheumatoid arthritis (RA) patients, persistent eosinophilia is observed. That can be due to the RA itself and is often associated with active disease and extra-articular features. Sometimes, it is attributed to the drug therapy, especially gold and penicillamine. We would like to report a 37-year-old female patient with HES who developed seronegative RA 2 years later.