Crude extract was obtained by light petroleum reflux extraction from exotesta of Ginkgo biloba L.,separated by silica gel column chromatography,and the mixture of ginkgolic acids(GA) could be obtained.Then the GA mixture was separated by repeated preparative chromatography,and six monomers could be obtained,namely:C(13∶0),C(15∶1),C(17∶2),C(15∶0),C(17∶1) and a novel compound.The purity of monomers reached more than 95%,and GA monomers could be used as reference samples for toxic GA analysis in G.biloba ...