A new compound was isolated from the traditional Chinese folk herb Crotalaria ferruginea. The structure of the new compound was identified as (±)-crotaferruphenol (1) based on analyses of its spectroscopic data including NMR, MS, and specific rotation values. (±)-Crotaferruphenol was a novel heterodimer characteristic of a unique spiroketal moiety, which was produced by the condensation reaction of a chromanone and a 2-isopropenybenzofuran. (±)-Crotaferruphenol exhibited inhibitory activity (IC50 = 6.57 μM.) against phosphodiesterase-4 (PDE4), a drug target for the treatment of chronic obstructive pulmonary disease and asthma.