Flavanones and chalcones bearing unusual isoprenoid side chains, and possessing antiulcer properties, have been isolated from several species of Sophora but so far S. secondiflora has been examined only because of the hallucinogenic alkaloids in its seeds. We find that it also contains, besides the known flavonoids liquiritigenin and calycosin, a new member of the relatively uncommon isoflavan series, unanisoflavan (1a), C₂₂H₂₆O₅, m.p. 184°, [α]₍D₎ (CHCl₃) -73.5, λ₍max₎ (EtOH) 286, 293 sh (log ε 3.7, 3.5), V₍max₎ (mull) 3500, 3300, 1600, 1620 cm⁻¹, which contains two phenolic OH groups, two OMe groups, and a 1,1-dimethylallyl side chain as shown by the n.m.r. spectrum. Hydrogenation of unanisoflavan gave the dihydro derivative (2a), selective methylation gave the phenolic ether (2b), and oxidation gave the isoflavanone (3). The structure of unanisoflavan (1a) was elucidated by spectral data (n.m.r., i.r., mass spectrum), chemical transformations, and molecular models, confirming its substituent distribution and core structure.