A bioassay-guided fractionation of the root extract of Angelica dahurica (Umbelliferae) led to the isolation of six furanocoumarins as active ingredients responsible for the antitumoral property. The hexane soluble part of the extract demonstrated a significant inhibition on the proliferation of cultured human tumor cells such as A549 (non small cell lung), SK-OV-3 (ovary), SK-MEL-2 (melanoma), XF498 (central nervous system) and HCT-15 (colon) in vitro, whereas the remaining water soluble part exhibited poor inhibition. Intensive investigation of the hexane soluble part of the extract yielded six furanocoumarins, i.e. isoimperatorin, cnidicin, imperatorin, oxypeucedanin, byakangelicol, oxypeucedanin hydrate, all of which exhibited a significant inhibition on cell proliferation in a dose-dependent manner.