Bucillamine (Buc) is a disease-modifying antirheumatic drug (DMARD) developed in Japan, which has been used as one of the first-line DMARDs for the treatment of rheumatoid arthritis (RA) in Japan. However, direct comparison of this drug with standard DMARDs including sulfasalazine (SASP) and methotrexate (MTX) has been scarcely reported. We therefore tried to evaluate the clinical efficacy of Buc by analyzing the database from the long-term observational cohort study IORRA (previously known as J-ARAMIS). The cross-sectional analysis revealed that responses to Buc treatment were better in males, patients with shorter duration of illness, and those who were rheumatoid factor-negative. In the longitudinal analysis, although there was no marked difference among the baseline variables of patients with Buc, SASP, and MTX, the percentage of patients exhibiting moderate or good response to treatment, as rated using the European League Against Rheumatism improvement criteria, was higher in the Buc group (41.0%) than in the MTX (32.6%) and SASP groups (25.6%). These data support Buc as a candidate for being a first-line drug for the treatment of patients with RA.