Objectives : The aim of this study was to investigate the effects of Ginseng Radix (Panax ginseng C.A. MEY.), Zizyphi Spinosae Semen (Zizyphus spinosa HU.) and Rehmanniae Radix Preparat (Rehmannia glutinosa LIBOSCH.) on the serotonin- immunoreactivity cells in the Caudal raphe nuclei, Rostal raphe nuclei and hippocampus of the mouse brain. Methods : The mice were stressed by restraining for one hour and treated with herbal medicine by oral feeding. The mice were killed after one hour and observed by electron microscope after immunohistochemical staining. Results : In the caudal raphe nuclei of the medulla oblongata, the highest number of 5-HT immunoreactivity cells were observed at the Zizyphi Spinosae Semen-treated group, while the lowest level among the herbs treatment group was shown at the Ginseng Radix group. In the hippocampus, serotonin-immunoreactive cells were expressed significantly at the CA3 area while the lowest level of it was shown at the control group. In the midbrain, immunoreactive cells were expressed higher than other groups, while observed at the lowest level in the control group. Conclusions : The extracts of Zizyphi Spinosae Semen, Rehmanniae Radix Preparat and Ginseng Radix show a certain degree of effect on the change of serotonin immunoreactive neurons as an index of nerve disorder.