To analyze the possible beneficial effects of statins on the disease activity of patients with rheumatoid arthritis (RA) using a database from a large observational cohort study. We studied a total of 7512 patients enrolled in a single-institute based prospective observational cohort of RA patients (IORRA); their information was collected biannually. In this study, cross-sectional data of 4152 patients (female 83.3%, average age 58.4 yrs) in October 2003 were analyzed (Mann-Whitney U-test). Among 4152 patients with RA, 279 (6.7%) were taking statins; patients taking statins had lower C-reactive protein (0.85 vs 1.24 mg/dl, respectively) and lower swollen joint counts (1.80 vs 2.55), but more frequently used corticosteroids (2.88 vs 2.40 mg/day) compared to patients not taking statins. Serum cholesterol level was closely related to the use of corticosteroids. Thus, an adjustment with the dose of corticosteroid was conducted; even taking account of the effects of steroids, RA disease activity indicated by patient's assessment for pain, physician's assessment, and swollen joint counts was significantly lower in patients with statins compared to those without. This study indicates that statins have beneficial effects in reducing RA disease activity in the daily practice of rheumatology.