OBJECTIVES: To analyze characteristics and to estimate costs of rheumatoid arthritis(RA) patients treated with TNF antagonist using the Korea national health insurance(KNHI) claims database between 2007 and 2009 from insurer’s perspective. METHODS: RA patients were identified as adults ( age of 19) who had at least one KNHI record with a diagnosis of RA (ICD-10 codes: M05-06) in 2007, 2008 and 2009. TNF antagonist naïve patients were defined as RA patients who didn’t have any claim record for a TNF antagonist during window period but who had records between Jul.1.2007 and Dec.31.2008. Socio-demographic and clinical characteristics, healthcare utilization, and costs were assessed for following 12 months. Direct medical costs included the total costs for medical services and drug costs except uninsured medical expenses. Multiple logistic regression was used to calculate the effects of several factors on the total costs. All statistical analyses were performed with SAS/STATⓇ 9.1. RESULTS: 48.9% of patients with at least one inpatient visit for 12 months. Annual average visit days of outpatients were 37. Annual overall costs per patient were 13.4 million Korean won (KRW), of which 10.5 million KRW (78.6%) was drug costs because of costly TNF antagonist. Inspection cost came next with 5.6% of the total costs, followed by hospitalization cost (4.6%), operation cost (4.0%), and doctor’s fee (3.2%). Mean out-of–pocket expenditure was 3.7 million KRW, 27.1% of the overall costs. As age increased, so did the total costs. Male, medical aid, and patients with hospitalization or surgery were associated with significantly higher costs than female, health insurance, and inexperienced patients of hospitalization or surgery respectively.(p<0.05) CONCLUSIONS:  Direct medical costs per capita of RA patients receiving TNF antagonist in Korea were 13.4 million KRW. The economic burden of RA patients is strongly influenced by TNF antagonist.