The quantitative content of flavonoid amount in aerial part of S. telephium L. and S. maximum (L.) Hoffm. is investigated. It was respectively 3.32% and 2.42% of the absolutely dry raw material mass. Antimicrobial activity of aqueous alco- holic extract of both species on Staphylococcus aureus ATCC 6538Р, Pseudomonas aeruginosa ATCC 27835, Escherichia coli ATCC 25922.