The purpose of this study is to compare the safety of NI-071 with Remicade® (infliximab) in patients with Rheumatoid Arthritis inadequately treated with Methotrexate.

Inclusion Criteria:

1. Diagnosis of Rheumatoid Arthritis (RA) as defined by the 1987 revised American College of Rheumatology (ACR) criteria with ACR Functional Classification class I-III and disease duration of no less than 3 months
2. Patients must receive a minimum of 3 months treatment with methotrexate (MTX) (≥ 6 mg/week) prior to the Screening Visit. Patients must be on a stable dose of MTX (6 mg~16 mg mg/week) for a minimum of 4 weeks prior to the Screening Visit

Exclusion Criteria:

1. History of following diseases

   • Other Connective tissue disorders with joint symptom which may interfere the efficacy assessment
   • Chlonic or recurrent infectious disease（bronchial ectasia, sinus inflammation etc.）
   • Severe infectious disease（hepatitis, pneumonia、sepsis）
   • History of demyelinating disease or multiple sclerosis
   • Congestive heart failure
   • lymphoproliferative disorder or myelodysplastic syndrome
   • History of malignancy
   • Interstitial lung disease

2. Patients with active or latent tuberculosis or history of tuberculosis