This study will evaluate the safety \& efficacy of Certolizumab Pegol (CZP) as additional medication to Methotrexate (MTX) in Chinese subjects with Rheumatoid Arthritis. 400 patients will be randomized to receive either CZP + MTX or placebo + MTX. Anticipated time in the study is about 32 weeks.

This is a phase 3, multicenter, double-blind, placebo-controlled, parallel group, randomized, 24-week study to evaluate the safety and efficacy of Certolizumab Pegol (CZP) as additional medication to Methotrexate (MTX) in Chinese subjects with active Rheumatoid Arthritis (RA) who have an incomplete response to Methotrexate. This study is designed to determine whether CZP 400 mg at Weeks 0, 2, and 4 followed by CZP 200 mg every 2 weeks (Q2W) in combination with MTX demonstrates superiority, in terms of greater improvement in relief of the signs and symptoms of RA, compared with MTX alone. Approximately 535 subjects will be screened to randomize 400 subjects into this study, at approximately 25 centers in the People's Republic of China. There will be 2 treatment groups, with 300 subjects in the CZP+MTX group and 100 subjects in the PBO+MTX group. For each subject, the study duration will last a maximum of approximately 38 weeks. Subjects who complete study RA0044 and subjects who fail to achieve an American College of Rheumatology 20 % Response Criteria (ACR20) response at Week 12 that is confirmed at Week 14 and thus are withdrawn from this study at Week 16, are permitted to receive treatment with CZP in the open-label extension study, RA0078. The secondary objectives are to assess the dose regimen of CZP in combination with MTX compared with MTX alone in the safety and tolerability, ability to improve physical function, and health outcomes measures in Chinese subjects with active RA; also to characterize the pharmacokinetic (PK) profile and immunogenicity of CZP in combination with MTX.