In other to elucidate the neuroprotective effects of Haeahwan on oxidant-induced neurotoxicity in cultured rat spinal motor neurons, the colorimetric assay such as MTT, NR, LDH, Lipid peroxidation was also carried out after cultured spinal motor neurons from neonatal rat were treated with the medium containing various concentrations of Methylmercuric chloride(MMC) for 8 hours. In addition, the protective effect of Haeahwan water extract extracts on the neurotoxicity induced by oxygen radicals was examined in these cultures. The results were as follows : 1.Survival rate of cultured spinal motor neurons were remarkably decreased by MMC depending on different kinds of concentrations. 2.NR50 of MMC as 50μM. 3.Haeahwan water extract inhibited significantly the increase in LDH activities induced by MMC.