Poria cocos is a well-known traditional Chinese traditional medicine (TCM) that grows around roots of pine trees in China, Korea, Japan, and North America. Poria cocos has been used in Asian countries to treat insomnia as either a single herb or part of an herbal formula. In a previous experiment, pachymic acid (PA), an active constituent of Poria cocos ethanol extract (PCE), increased pentobarbital-induced sleeping behaviors. The aim of this experiment was to evaluate whether or not PCE and PA modulate sleep architectures in rats as well as whether or not their effects are mediated through GABAA-ergic transmission. PCE and PA were orally administered to individual rats 7 days after surgical implantation of a transmitter, and sleep architectures were recorded by Telemetric Cortical encephalogram (EEG) upon oral administration of test drugs. PCE and PA increased total sleep time and non-rapid eye movement (NREM) sleep as well as reduced numbers of sleep/wake cycles recorded by EEG. Furthermore, PCE increased intracellular chloride levels, GAD65/67 protein levels, and α-, β-, and γ-subunits of GABAA receptors in primary cultured hypothalamic neuronal cells. These data suggest that PCE modulates sleep architectures via activation of GABAA-ergic systems. Further, as PA is an active component of PCE, they may have the same pharmacological effects.