Six gamma-glutamyl oligopeptides were isolated for the first time from aqueous methanol extracts of Panax ginseng root by using column chromatography on ion-exchange resin, gel filtration and reverse-phase high-performance liquid chromatography. Their structures had been established with the methods of amino acid analysis, N-terminal, C-terminal determination and double-coupling sequence analysis. They were: P-I (N-gamma-glutamylcystinyl-bis-glycine), P-ll (gamma-glutamylcysteinylglycine disulfide, oxidized glutathione), P-III (N,N'-bis-gamma-glutamylcystinylglycine), P-IV (gamma-glutamylcysteinylglycinamide disulfide), P-V (N-gamma-glutamylglycylcysteine disulfide), P-VI(gammaglutamylarginine); five of them are related to oxidized glutathione. The structures were further confirmed by the chemical synthesis. As far as we know, P-V (N-gamma-glutamylglycylcysteine disulfide) is a new biologically active peptide which exhibits somnogenic effect and is more potent than that of P-II.