[Purpose] Kamishoyosan (KSS) is a Japanese herbal medicine that is said to be effective for frustration, but the detailed mechanism is unknown. In this study, we analyzed the action of KSS using a mouse aggressive response measuring device (ARM). [Method] In this study, 3-week-old ddY strain mice were isolated and reared one by one until 10-week-old, and individuals showing a constant biting strength (7 to 15 mNs) were used. KSS powder (Tsumura, TJ-24, 100 mg/kg) was suspended in physiological saline and administered by intraperitoneal injection, and the bite strength and frequency before and after administration were compared by using ARM. We also compared the bite intensity and frequency in mice to which the estrogen receptor inhibitor tamoxifen (5 mg/kg) was administered 30 minutes before the administration of KSS. Brain tissue was excised 2 hours after administration of KSS and used for quantitative PCR analysis of Esr2 mRNA encoding estrogen receptor β (ERβ). [Results] Two hours after administration of KSS, the biting strength decreased by about 48% in females and about 56% in males (p <0.05). In the mice to which Tamoxifen (5 mg/kg) was previously administered, no significant decrease was observed even after administration of KSS. In the mouse brain (dorsal raphe nuclei) after administration of KSS, the amount of Esr2 mRNA increased by about 1.27 times in females and about 1.35 times in males compared to mice administered with saline (p <0.05). [Discussion] In this study, it was found that the aggressive behavior that occurred in isolated-reared mice was reduced by administration of KSS. In addition, the involvement of ERβ is suggested in this action.