The study is to investigate the effect of asiaticoside on collagen-induced arthritis (CIA). The model of CIA mice was prepared and the change of secondary paw swelling and the arthritis scores were observed. In vitro proliferation of spleen cells was examined using MTT assay. The cell-free protein extracts from the arthritic joints and nonarthritic joints were used for the analysis of protein expression of cyclooxygenase-2 (COX-2). And the level of PGE2 in joints was assayed using PGE2 express EIA kit. The tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) levels in the serum were measured by ELISA. Histopathological examination was performed by hematoxylin-eosin (HE) stain method. Asiaticoside (10, 20 and 40 mg x kg(-1) x d(-1), 22 d, ig) significantly reduced paw swelling, and decreased the arthritis scores. There was a significant reduction in proliferation of spleen cells of CIA mice treated with asiaticoside as compared with that of untreated CIA mice. COX-2, PGE2, TNF-alpha and IL-6 production in CIA mice were inhibited by asiaticoside. Meanwhile, the pathological examination showed that articular cartilage degeneration with synovial hyperplasia and inflammatory cells infiltration in CIA mice was suppressed by asiaticoside. Its active mechanism may be related to inhibiting proliferation of lymphocyte and reduction of expression of COX-2 and inflammatory cytokines.