A new natural substance, cordoin, C₂₀H₂₀O₃, was isolated from Cordoa placa (genus Lonchocarpus) a plant growing in North East Brazil. Through the physico-chemical properties (u.v., ir. and nmr spectra) and mass fragmentation pattern, and the chemical reaction the structure of $2^{\prime}hydroxy-4^{\prime}-\gamma-\gamma-dimethyl-allyloxy-chalcone$ was attributed to cordoin. This is the first example of O-prenylated chalcone found in nature. Its presence in Lonchocarpus may account for the biogenesis of rotenoids.