Background: A combination of conventional disease-modifying anti-rheumatic drugs improves the treatment of rheumatoid arthritis but with high side-effects. Methotrexate (MTX) combination therapy that with high therapeutic efficacy and low toxicity is in demand in many countries to replace the use of expensive biological agents. Study design: This study was an open-label, 24-week, parallel randomized controlled trial conducted between November 2015 and December 2017. Methods: Patients were randomly assigned at a 3:2 ratio to receive MTX combined with sinomenine (SIN) at a dose of 120 mg twice daily, or leflunomide (LEF) at a dose of 20 mg once daily. Efficacy and safety were assessed at weeks 4, 12 and 24. The primary efficacy endpoint was the proportion of patients achieving an American College of Rheumatology (ACR)50 response and a European League Against Rheumatism (EULAR) good response at week 24. Results: A total of 101/120 (84.2%) patients completed 24 weeks of observation. In the intention-to-treat (ITT) analysis, 65.3% of patients treated with MTX + SIN showed improved disease activity as determined by the ACR50 response at week 24 compared to 69.6% of patients treated with MTX + LEF. A similar insignificant pattern was found for the ACR20 and ACR70 responses, as well as the clinical disease activity index, EULAR response, and remission and low disease activity rates between these two treatment groups. The per-protocol analysis showed results consistent with those of the ITT analysis. Notably, significant reductions in gastro-intestinal adverse reactions and liver toxicity were found in patients treated with MTX + SIN compared to patients treated with MTX + LEF (p < 0.05). Conclusion: Considering the balance of efficacy and toxicity, the current study provides evidence that MTX + SIN combination therapy is probably one of the choices for treating patients with active rheumatoid arthritis in addition to MTX + LEF combination therapy.