Abstract: In a program of screening antibiotics from natural products,an antifungal ingredient was obtained from the fermentation broth of Colletotrichum orbiculare by the procedure of macroporous resin extraction and silica column chromatography.Its chemical structure was elucidated by the techniques of HR-ESI MS,NMR and IR,and its antifungal activity against Botrytis cinerea,Fusarium oxysporum,Alternaria alternata,Colletotrichum gloeosporioides and Curvularia lunata was evaluated by the methods of inhibition of spore germination and mycelium growth,respectively.The results indicated that the active ingredient was radiciol,a member of resorcylic acid lactone family.Rediciol could not inhibit the spore germination of all tested fungi,whereas it showed strong inhibitory activity against mycelial growth of B.cinerea.