Artemisia capillaris Thunb. is widely used in the herbal medicine field. This study describes the antidepressant effect of a flavonoid (chlorogenic acid) isolated from the Artemisia capillaris Thunb. The expression of the pituitary gland and hypothalamic POMC mRNA or plasma ${eta}$-endorphin levels were increased by extract of Artemisia capillaris Thunb. or its flavoniod administered orally. In addition, antidepressant activity was studied using the tail suspension test (TST), the forced swimming test (FST) and the rotarod test in a chronically restrained immobilization stress group in mice. After restraint stress (2 h/day for 14 days), animals were kept in a cage for 14 days without any further stress, but with drugs. Mice were fed with a diet supplemented for 14 days and during the behavioral test period with chlorogenic acid (30 mg/kg/day). POMC mRNA or the plasma ${eta}$-endorphin level was increased by the extract of Artemisia capillaris Thunb. and its flavoniod. In addition, the immobility time in TST and FST was significantly reduced by chlorogenic acid. In the rotarod test, the riding time remained similar to that of the control group at 15 rpm. Our results suggest that the flavonoid (chlorogenic acid) isolated from Artemisia capillaris Thunb. shows a potent antidepressant effect.