Collagen-induced arthritis (CIA) is a model for some types of human autoimmune rheumatoid arthritis (RA). In this study, we examined whether ethanol extract of potato (Solanum tuberosum) is efficacious against CIA in mice. Potato extracts (100 and 200 mg/kg) were orally administered to DBA/1J mice once daily for 49 day after initial immunization with type Ⅱ collagen. Clinical assessment of disease and measurement of paw edema were conducted throughout the study. The production of CIA-related rheumatoid factor, anti-type Ⅱ collagen antibody, and cytokines were examined in DBA/1J mice.