The expression and activity of NF-kappaB in the synovium of collagen-induced arthritis (CIA) rats was detected in order to investigate the possible therapeutic effects of triptolide on rheumatoid arthritis (RA). The experimental Wistar rat model of CIA was set up by intradermal injection of emulsion of bovine collagen II and the successful rate of setting-up models was evaluated by arthritis index (AI). Rats were grouped randomly into three groups: normal, model and treatment group. The expression of TNF-alpha and IL-6 in synovial fluid was detected by ELISA, and the expression and activity of NF-kappaB in synovium by immunohistochemistry method and by electrophoretic mobility shift assay (EMSA) respectively. As compared with normal group, the expression of TNF-alpha and IL-6 in synovia (P < 0.05), and the expression and activity of NF-kappaB (P < 0.05) in synovium were increased in model group. There was statistical difference in above-mentioned indexes between model group and treatment group. Triptolide may play a protective role in RA via downregulating the expression and activity of NF-kappaB in synovium.