Polygalae radix (PR) has traditionally been used as a sedative and anti-stress agent in oriental countries for a long time. PR which contains many ingredients is especially rich in saponins. This study was performed to investigate whether ethanol extract of PR enhances pentobarbital-induced sleep behaviors. In addition, possible mechanisms also were investigated. PR inhibited locomotor activity in mice. PR increased sleep rate and sleep time by concomitant administration with sub-hypnotic dose of pentobarbital (28 mg/kg). PR prolonged total sleeping time, and shortened sleep latency induced by pentobarbital (42 mg/kg). In addition, PR increased intracellular chloride concentration in primary cultured neuronal cells. The expression level of glutamic acid decarboxylase (GAD) were increased, and ${gamma}$-aminobutyric acid $(GABA)_A$ receptors subunits were modulated by PR, especially increasing ${gamma}$-subunit expression. In conclusion, PR augments penobarbital-induced sleep behaviors through activation of $GABA_A$ receptors and chloride channel complex.