The effect of Ganoderma total sterol (GS) and its main components(GS(1)) on rat cortical neuronal cultures exposed to hypoxia/reoxygenation (H/R) was studied in vitro. GS (0.01,0.1,1 microg/ml) increased neuron viability following H/R. GS also significantly reduced malondialdehyde content and reactive oxygen species production and increased manganese superoxide dismutase (Mn-SOD) activity; furthermore, the translocation of nuclear factor-kappa B and the production of interleukin-1beta and tumor necrosis factor alpha induced by H/R were also blocked. These findings suggest that GS might be useful in treating H/R-induced oxidative stress and inflammatory response. We also hypothesized that Mn-SOD might play a critical role in the neuroprotective effect of GS against H/R injury. In addition, pretreatment with GS(1) (0.01, 0.1, 1 microg/ml) significantly attenuated the decline of neuron viability and the formation of reactive oxygen species. Furthermore GS(1) possessed more potent protective effect on neurons compared with GS at the same dose. These findings demonstrated that GS(1) is the main component in GS; and play a critical role in the neuroprotective effect of GS against H/R.