Microglia are believed to participate in the mediation of neurodegeneration through producing a variety of cytotoxic factors upon activation. Pharmacological intervention in microglial activation may therefore exert a neuroprotective effect. In exploring pharmacological agents that can affect microglial activation, we found in this study that triptolide possesses a powerful inhibitory influence over microglia. Pretreatment with triptolide was able to dose-dependently reduce the lipopolysaccharide (LPS)-induced nitrite accumulation and tumor necrosis factor-alpha and interleukin-1beta release from LPS-activated microglia as revealed by Griess reaction and ELISA, respectively. Triptolide reduced LPS-stimulated mRNA expression of all three inflammatory factors. The results obtained from this study demonstrate that triptolide can inhibit inflammatory responses of microglia to inflammatory stimulation via a mechanism involving the inhibition of the synthesis and release of inflammatory factors.