Reaction of quercetin (QR) (1) with bromine under various conditions was studied. Interaction of QR with 2-3 equiv. of bromine in glacial acetic acid at 35-40°C for 2-4 h and 20-22°C for 24 h led to the formation of QR 6,8-dibromide (2) (52-54% yields, 96-98% purity by HPLC). Interaction of QR with 2-5 equiv. bromine in absolute ethanol at 0-5°C and 20-22°C for 24 h led to the formation of 3-O-ethyl-QR-2,3,6,8,5'-pentabromide (3) (95-97% purity by HPLC) the output of which depends on the quantity of bromine. It was shown in MDCK cell culture that compound 2 exhibits a moderate inhibitory activity against pandemic influenza virus A/H1N1/pdm09 (EC50 6.0 µg/mL, CTD50 97.7 µg/mL, SI 16). Compound 3 was inactive.