Abstract: Thirteen isoflavones were separated and purified from an ethanol extract of the rhizome of Dalbergia benthamii Prain by using silica gel, Sephadex LH-20, recrystallization et al. Their structures were identified by physicochemical properties and spectral analysis such as MS, 1D/2D-NMR as dalbergibenthamin (1), butesuperin A (2), xanthocercin A (3), butesuperin B (4), di-O-methylalpinum isoflavone (5), 2′-deoxgisoaunculutin (6), robustone (7), 4′-hydroxy-5, 7-dimethoxy-6-(3-methyl-2-butenyl)-isoflavone (8), formononetin (9), 6″-O-rhamnosyldaidzin (10), 3′, 4′-di-O-methylene-5-hydroxy-7-methoxy-6-isopentenyl isoflavone (11), derrubone dimethyl enter (12), and derrubone (13). Compound 1 is a pair of new isoflavonoid enantiomers, compound 12 is a new natural product and compounds 1-7 and 10-13 were obtained from D. benthamii Prain for the first time. In vitro cytotoxic activities of the compounds were explored by MTS testing with HL-60, A-549, SMMC-7721, MCF-7 and SW480 cell lines. Results show that compound 8 significantly inhibited cellular proliferation. The IC₅₀ of compound 8 in A-549 and SW480 cells was 16.68 ± 0.19 and 15.21 ± 0.60 μmol·L^-1.