Gagamguibitang, a composite Korean medicinal drug prescribed by us, was evaluated for its sedative effects by measurements of potentiation on pentobarbital-induced sleeping time, anticonvulsive activities in animal model, inhibitory effect on GABA transaminase activity, and antioxidative activities in vitro- and/or in vivo assay. The results were summerized as follows : 1. Gagamguibitang showed about 2-fold prolongation of pentobarbital-induced sleeping time compared to the control group after administration(p.o) with 2.0g/kg of mice body weight. 2. Gagamguibitang strongly lengthened onset time of pentylenetetrazole-induced convulsion, shortened the duration of convulsion and diminished the lethality after treatment(p.o) with 1.0g/kg of mice body weight. 3. Gagamguibitang inhibited dose-dependently the brain GABA transaminase activity in vitro compared to the control group and in vivo compared to the pentylenetetrazole-treated group. 4. Gagamguibitang inhibited effectively brain lipid peroxidation by 45.8% at a dose of l0mg/ml in vitro and by 47.5% after oral treatment with 0.5g/kg of mice body weight in vivo assay. 5. Gagamguibitang exhibited a potent scavenging activity on DPPH radical in a dose-dependent manner with ca. 92% activity at l0mg/ml. As a result, Gagamguibitang can be useful for the effective sedative drug in clinical application.