Rheumatoid arthritis (RA) is an inflammatory disorder characterized by oxidative stress, inflammation and cartilage destruction. Withania somnifera (WS) is used in Indian folk medicine for the treatment of various musculoskeletal disorders. WS is considered to possess potent antioxidant and anti-inflammatory activities. The aim of the present study was to evaluate the possible mechanism of action of methanolic extract of Withania somnifera roots (WSMe) against collagen induced arthritic (CIA) rats. Arthritis in rats was induced by subcutaneous injection of bovine type II collagen and was treated with WSMe at the dose of 200 mg/kg BW for 20 days after arthritis was induced. Number of biochemical, molecular and histological changes was observed in CIA rats. In CIA rats we found an imbalance in antioxidant and oxidant status as level of MDA was increased while GST, GSH and FRAP was found to be decreased. Administration of WSMe200 significantly ameliorates the level of antioxidant and oxidant to near normal. Serum concentration of transcription factor NF-kB, inflammatory cytokines like TNF-α, IL-1β, IL-6 and IL-10 were altered in CIA rats. In consistent to this mRNA expression of NF-kB, TNF-α and MMP-8 were also found to be Up-regulated, which were significantly inhibited by WSMe200 treatment. These findings are positively correlated with the results of histological examinations of joints, which showed reduced inflammation and bone erosion in the treated group. The ability to inhibit the production of oxidative stress and subsequent modulation of the inflammatory cytokines shows the protective effect of WSMe and its potential use for the treatment of arthritis.