Combining chemical and microbiological methods using entomopathogenic filamentous fungi makes obtaining flavonoid glycosides possible. In the presented study, biotransformations were carried out in cultures ofBeauveria bassianaKCH J1.5,Isaria fumosoroseaKCH J2, andIsaria farinosaKCH J2.6 strains on six flavonoid compounds obtained in chemical synthesis. As a result of the biotransformation of 6-methyl-8-nitroflavanone using the strainI. fumosoroseaKCH J2, two products were obtained: 6-methyl-8-nitro-2-phenylchromane 4-O-β-D-(4″-O-methyl)-glucopyranoside and 8-nitroflavan-4-ol 6-methylene-O-β-D-(4″-O-methyl)-glucopyranoside. 8-Bromo-6-chloroflavanone was transformed by this strain to 8-bromo-6-chloroflavan-4-ol 4′-O-β-D-(4″-O-methyl)-glucopyranoside. As a result of microbial transformation byI. farinosaKCH J2.6 effectively biotransformed only 8-bromo-6-chloroflavone into 8-bromo-6-chloroflavone 4′-O-β-D-(4″-O-methyl)-glucopyranoside.B. bassianaKCH J1.5 was able to transform 6-methyl-8-nitroflavone to 6-methyl-8-nitroflavone 4′-O-β-D-(4″-O-methyl)-glucopyranoside, and 3′-bromo-5′-chloro-2′-hydroxychalcone to 8-bromo-6-chloroflavanone 3′-O-β-D-(4″-O-methyl)-glucopyranoside. None of the filamentous fungi used transformed 2′-hydroxy-5′-methyl-3′-nitrochalcone effectively. Obtained flavonoid derivatives could be used to fight against antibiotic-resistant bacteria. To the best of our knowledge, all the substrates and products presented in this work are new compounds and are described for the first time.