The debate regarding the influence of body mass index (BMI) on clinical disease activity in rheumatoid arthritis (RA) remains unsolved. This study investigates whether BMI is associated with disease activity composites and clinical parameters in Korean patients with RA. A total of 568 patients with RA were consecutively enrolled in this study. BMI and disease activity composites including the Disease Activity Score 28 (DAS28) and the Clinical/Simplified Disease Activity Index (CDAI/SDAI) were assessed. Statistical analyses were performed using Chi-square, one-way ANOVA, and multivariate regression analyses. Remission of RA disease activity was defined as ≤2.6 in a DAS28 score. The mean BMI was 22.3 kg/m(2) (SD 3.1). About 60.6 % (n = 344) of enrolled patients fell into the underweight and normal BMI categories. Swollen joint count was significantly different among the four BMI categories (p = 0.038). Multivariate regression analysis showed a negative correlation of BMI and erythrocyte sediment rate (ESR) in all patients (β= - 0.011, p = 0.049) and also found that other disease activity indices were not found to be associated with BMI. In patients with remission, lower BMI was associated with higher physician global estimate (β= - 0.446, p = 0.030). The negative association between BMI and ESR in the non-remission group was noted (β= - 0.016, p = 0.019). This study revealed lack association between BMI and disease activity composites of RA, although only ESR was found to be associated with BMI in RA patients.