Objective: To determine the real-world safety and effectiveness of iguratimod (IGU) for rheumatoid arthritis (RA), a 52-week, Japanese, post-marketing surveillance study was conducted. An interim analysis at week 24 was performed.Methods: This study included all RA patients who received IGU following its introduction to the market. All adverse events (AEs) and adverse drug reactions (ADRs) were collected. Effectiveness was evaluated by the change in Disease Activity Score 28-C-reactive protein (DAS28-CRP) from baseline to week 24.Results: Safety was analyzed in 2679 patients. The overall incidences of AEs, ADRs, and serious ADRs were 38.41, 31.65, and 3.21%, respectively; the most commonly reported serious ADRs were pneumonia/bacterial pneumonia, interstitial lung disease, and Pneumocystis jiroveci pneumonia. Concomitant glucocorticoid use and comorbid conditions associated with respiratory disease were identified as risk factors for serious infections. Pulmonary alveolar hemorrhage and increased international normalized ratio of prothrombin time were observed with concomitant use of IGU and warfarin. The DAS28-CRP decreased from baseline to week 24.Conclusion: Although a safety concern was identified with concomitant use of IGU and warfarin, this real-world study showed no other new safety concerns and similar effectiveness to clinical trials. IGU is a new therapeutic option for RA patients.