Microbial transformations of isoxanthohumol (1), a beer prenylated flavonoid, by 51 fungi were investigated. Many of the tested fungi cultures were capable of effective transformation of 1. Mucor hiemalis and Fusarium oxysporum converted isoxanthohumol (1) into isoxanthohumol 7-O-β-d-glucopyranoside (3) and (2R)-2″-(2″'-hydroxyisopropyl)-dihydrofurano[2″,3″:7,8]-4″,5-hydroxy-5-methoxyflavanone (4), respectively. No product was obtained in the transformation of 1 by Absidia glauca conducted in a phosphate buffer. In the same medium, Beauveria bassiana converted isoxanthohumol (1) to isoxanthohumol 7-O-β-d-4″'-O-methylglucopyranoside (2).