To elucidate the toxic effect of oxygen free radicals on cultured mouse spinal motor neurons damaged by hydrogen peroxide(H₂O₂)-induced neurotoxicity, we examined the neurotoxicity induced by oxygen radicals by NR assay when cultured spinal motor neurons were grown in the medium containing various concentrations of H₂O₂ for 6 hours. In addition, neuroprotective effects of herb extracts such Rhizoma Gastrodiae(RG), on H₂O₂-induced neurotoxicity in cultured spinal motor neurons were evaluated after cultured spinal motor 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 extract, RG increased cell viability of spinal motor neurons damaged by H₂O₂ in these cultures. From the above results, it is suggested that H₂O₂ was toxic in cultured spinal motor neurons derived from mouse, and RG was effective in blocking the neurotoxicity induced by oxidative stress in these cultures.