Bupleuri radix (Umbelliferae), the dried root of Bupleurum Chinense DC, has been clinically used tomitigate pain sensation. The descending pain control system consists of three major components,and modulation of pain in the periaqueductal gray is the most extensively studied descendingpain control system. However, the relation of Bupleuri radix on the descending pain controlsystem has not been clarified. In the present study, modulation of the aqueous extract of Bupleuriradix on glycine-induced ion current in the acutely dissociated periaqueductal gray neurons wasinvestigated by using nystatin-perforated patch-clamp technique under voltage-clamp condition.In the present results, the glycine-induced ion current was significantly suppressed by 0.1 mg/mlBupleuri radix, while treatment with 10-5 M naltrexone, opioid receptor antagonist, alleviatedBupleuri radix-induced inhibition on glycine-induced ion current. The present study showed thatthe aqueous extract of Bupleuri radix may activate descending pain control system throughinhibition on glycine-induced ion current in the periaqueductal gray neurons and this effect ismediated by opioid receptors.