This study aimed to investigate the effects of obovatol isolated from Magnolia obovata on pentobarbital-induced sleeping behaviors and to determine whether these effects were mediated by GABA A receptors/chloride channel activation, using a western blot technique and Cl − sensitive fluorescence probe. GABA A receptors subunits expression and chloride influx were investigated in cultured cerebellar granule cells. Obovatol (0.05, 0.1, and 0.2mg/kg) prolonged the sleeping time induced by pentobarbital (42mg/kg). In addition, obovatol (20 and 50μM) significantly increased Cl − influx in the primary cultured cerebellar granule cells. Moreover, obovatol increased the expression of GABA A receptor α-, β-, and γ-subunits. However, it had no effect on the abundance of the expression of glutamic acid decarboxylase (GAD), suggesting that obovatol might not activate GAD. These results suggest that obovatol potentiates pentobarbital-induced sleeping time through the GABA A receptors/chloride channel activation.