The ether soluble fraction of the roots of Angelicae gigantis Radix caused a significant prolongation of hexobarbital(HB) induced sleeping time in mice. Through systematic fractionation of the ether fraction monitored by bioassays, two pyranocoumarins, decursinol angelate and decursin were isolated as active principles. Decursin, as a main component, exhibited significant prolongation of HB-induced hypnosis as well as significant inhibition of hepatic microsomal drug metabolizing enzyme(DME) activities at relatively high dose which indicated that it is a weak DME inhibitor.