The methylene chloride extract of the root of Angelicae dahuricae showed high protective activity against 2,2'-azobis (2-aminodinopropane) dihydrochloride (AAPH)-induced cellular damage. From this extract, 11 furanocoumarins were isolated, namely oxypeucedanin hydrate, 9-hydroxy-4-methoxypsoralen, byakangelicin, pabulenol, alloisoimperatorin, neobyakangelicol, byakangelicol, oxypeucedanin, imperatorin, phellotorin and isoimperatorin, respectively. Among these 11 furanocoumarins, 9-hydroxy-4-methoxypsoralen and alloisoimperatorin displayed potent antioxidant effects against the DPPH radical and against renal epithelial cell injury by using AAPH to generate peroxyl radicals in vitro.