The aim of the present study was to examine the effect of simultaneous mother-offspring administration of Yokukansan (YKS), a traditional Japanese herbal medicine, on the emotional abnormality induced by prenatal stress in mice. The dry powder extract of YKS used in the present study was supplied by Tsumura & Co. (Tokyo, Japan). YKS was mixed with powdered rodent chow at a concentration of 3% and fed to mice from birth until they reached 7 weeks of age. We then examined the effect of treatment with YKS on emotional abnormality induced by prenatal restraint stress. The open field test revealed that mice exposed to prenatal stress exhibited a significant decrease in the time spent in the central area, and this anxiety-like behavior was suppressed by YKS treatment. The expression levels of dopamine D2 receptors were significantly increased in the hippocampus and prefrontal cortex of mice exposed to prenatal stress, and these changes reduced to the same level as the control group by treatment with YKS. Additionally, similar results were obtained for the serotonin transporters in the prefrontal cortex. These results suggest that simultaneous mother-offspring administration of YKS could ameliorate increased anxiety sensitivity in offspring induced by prenatal stress by affecting the function of the monoamine system.