To assess the clinical efficacy as well as safety profiles of Leining, a novel cytotoxic T-lymphocyte antigen-4 fusion protein, versus placebo in the treatment of Chinese active rheumatoid arthritis (RA) patients with an inadequate clinical response to methotrexate (MTX). In this 24-week, randomized, double-blind, placebo-controlled multicenter study, a total of 440 Chinese patients with active RA with an inadequate response to MTX were randomly assigned to receive Leining (10 mg/kg) or placebo. Clinical response was assessed using the American College of Rheumatology 20 % improvement criteria ACR20, ACR50, and ACR70, with ACR20 as the primary major endpoints. Disease activity scores in 28 joints with erythrocyte sedimentation rate assessment (DAS28-ESR) were used to evaluate disease activity. After 24 weeks of treatment, significantly more patients in Leining group achieved ACR20 response than those in placebo group (70.61 vs. 46.36 %; p < 0.001). Similarly, ACR50 and ACR70 responses of Leining group were significantly higher than those of placebo group (40.30 vs. 22.73 %; p < 0.001 and 16.67 vs. 7.27 %; p < 0.05, respectively). DAS28-ESR in Leining group was significantly reduced compared to that in placebo group, with greater clinically meaningful (> 1.2 unit) improvement (54.85 vs. 29.09 %, p < 0.05). Both the rates of remission (DAS28-ESR < 2.6) and low disease activity (DAS28-ESR < 3.2) were greater in the Leining group than those in the placebo group (12.42 vs. 2.73 %; p < 0.05 and 15.45 vs. 2.73 %; p < 0.05 respectively). The overall incidence of adverse events was similar in both Leining and placebo groups. No neutralizing antibodies were detected. Leining demonstrated clinically meaningful efficacy compared with placebo in Chinese patients with active RA despite MTX therapy. Administration of Leining in combination with MTX for 24 weeks was well tolerated.