To elucidate the toxic effect of oxygen free radicals on cultured mouse cerebral neurons damaged by hydrogen peroxide(H₂O₂)-induced neurotoxicity, we examined the neurotoxicity induced by oxygen radicals by NR assay when cultured cerebral neurons were grown in the media containing various concentrations of H202 for 6 hours. In addition, neuroprotective effects of herb extracts such Rhizoma Gastrodiae(RG) on H202-induced neurotoxicity in cultured cerebral neurons were evaluated after cultured cerebral neurons were preincubated with various concentrations of herb extract, RG for 2 hours before 50uM H₂O₂ for 6 hours. H₂O₂ decreased remarkably cell viability in dose-and time-dependent manner in these cultures, and also herb exract, RG decreased LDH activity of cerebral neurons damaged by H₂O₂. From the above results, it is suggested that H₂O₂ was toxic in cultured cerebral neurons from mouse, and RG was effective in blocking the neurotoxicity induced by oxygen radicals in these cultures.