To evaluate the effect of Yuldahansotang(YHT) water extract on cultured hippocampal cell was inhibited by hydrogen peroxide, MTT assay, NR assay, Neurofilament enzymeimmuno assay and DNA synthesis assay were carried out after the cultured hippocampal cells were preincubated with various concentrations of YHT water extract for 3 hours prior to exposure of hydrogen peroxide. The results obtained were as follows: 1. Hydrogen Peroxide decreased the survival rate of the cultured hippocampal cells on NR assay and MIT assay. 2. YHT water extract have efficacy of increasing a amount of neurofilament decreased by hydrogen peroxide in cultured hippocampal cells. 3. YHT water extract have efficacy of increasing DNA synthesis decreased by hydrogen peroxide in cultured hippocampal cells. From above the results, It is concluded that YHT has marked efficacy in preventing for the damages by hydrogen peroxide.