Allergy-preventive activity was demonstrated for an extract of resins from Xanthorrhoea hastilis R. BR. in a search for allergy-preventive substances from natural sources. By bioassay-directed fractionation of this plant extract, a new flavanone, 3,5-dihydroxy-7,4-dimethoxyflavanone (1), and two new chalcones, 3,5,2-trihydroxy-4,4-dimethoxychalcone (2) and 5,2-dihydroxy-3,4,4-trimethoxychalcone (3), were isolated together with five known compounds, 5-hydroxy-7,3,4-trimethoxyflavanone (4), 3-hydroxy-7,4-dimethoxyflavanone (5), liquiritigenin 7-methyl ether (6), 4,2-dihydroxy-4-methoxychalcone (7) and sakuranetin (8). The structures of 1, 2 and 3 were elucidated by spectroscopic methods. All of these compounds showed allergy-preventive effects.