Flavonoids are a heterogeneous family of low molecular weight polyphenolic compounds synthesized in plants as secondary plant metabolites. They belong to phytochemicals and are found in fruits and vegetables. Regular consumption of individual flavonoids shows the potential for human health modification in helping to prevent chronic and degenerative diseases. Their numerous pharmacological effects make them interesting for research in the field of pharmacy. Mechanisms of their numerous biological effects are still largely unknown. Cytochromes P450 are undoubtedly the most important enzymes that catalyze the biotransformation of drugs. By sequencing the human genome, it has been found that there are 57 cytochrome P450 enzymes in humans. The field of biochemistry and cytochrome P450 enzymology remains attractive, with many open questions to be addressed, including the metabolism of flavonoids researched on a relatively small number of flavonoids. The aim of this paper is to determine in vitro the cytochromes P450 responsible for the biotransformation of 30 selected flavonoids using human liver microsomes. Reverse-phase high performance liquid chromatography with a mass spectrometer as a detector was asued as the method of screening. Of the analyzed 30 flavonoids, 11 showed the tendency of biotransformation mediated by cytochrome P450. The flavonoids whos metabolisms were described for the first time are: flavone, 7-hydroxyflavone, galangine, 3,7-dihydroxyflavone, 6-hydroxyflavone, acacetin and tangeretine metabolites.