The purpose of this study is to examine the toxic effects caused by xanthine oxidase/hypoxanthine(XO/HX) and the effects of herbal extracts such as Cheongsimyeonjatang(CYT) on the treatment of the toxic effects. For this purpose, experiments with the cultured hippocampal cells from new born mice were done. The results of these experiments were as follows. 1. XO/HX, a oxygen radical-generating system, decreased the survival rates of the cultured cells on MTT assay and NR assay, protein synthesis, and amounts of neurofilaments. 2. CYT have the efficacy of increasing protein synthesis decreased by XO/HX. 3. CYT have the efficacy. of increasing the amount of neurofilaments decreased by XO/HX. From the above results, it is suggested that Cheongsimyeonjatang (CYT) have marked efficacy as a protection for the damages caused by the XO/HX-mediated oxidative stress.