text: Ginseng, the root of Panax ginseng C. A. MEYER, has been used as a food product and medicinal ingredient. In this study, we assessed the anti-arthritic effects of red ginseng saponin extract (RGSE), including ginsenosides Rg3, Rk1 and Rg5 as major components, on a murine type II collagen (CII)-induced arthritis (CIA), which is a valid animal model of human arthritis. Oral administration of RGSE at 10 mg/kg reduced the clinical arthritis score and paw swelling in the CIA mice, and inhibited joint space narrowing and histological arthritis, illustrating the severity of synovial hyperplasia, inflammatory cell infiltration, pannus formation, and erosion of cartilage. RGSE inhibited the expression of matrix metalloproteinase-3 and nitrotyrosine formation, and recovered the expression of superoxide dismutase in the joints of the CIA mice. Orally administered RGSE also reduced the levels of serum tumor necrosis factor-alpha and interleukin-1beta in the CIA mice. CII- or lipopolysaccharide-stimulated cytokine production, in addition to CII-specific proliferation, was reduced in the spleen cells of the RGSE-treated CIA mice, as compared with those from vehicle-treated CIA mice. Furthermore, RGSE administration protected against CIA-induced oxidative tissue damage by restoring the increased malondialdehyde levels and the decreased glutathione levels and catalase activities almost to control levels. Therefore, RGSE may be a beneficial supplement which can improve human arthritis.