Rheumatoid arthritis (RA) is the most common form of chronic inflammatory arthritis characterized by pain, swelling and destruction of joints, with a resultant disability. Disease-modifying anti-rheumatic drugs (DMARDs) and biological drugs can interfere with the disease process. In this study, the effect of β-d-mannuronic acid (M2000) as a novel non-steroidal anti-inflammatory drug (NSAID) with immunosuppressive and anti-inflammatory effects together with antioxidant effects was evaluated on