TLC analysis of Knautia arvensis demonstrated phenolcarboxylic acids and flavonoids. Spectrophotometric studies were run to assess the quantitative composition of phenolic compounds expressed as chlorogenic acid (from 1.05% to 2.08%), and it was proposed that this substance can be used for standardization of samples of Knautia arvensis herb. HPLC-UV identified the presence of o-coumaric, gallic, neochlorogenic, chlorogenic, caffeic, isoferulic, and rosmarinic acids, as well as hyperoside and kaempferol. Chlorogenic acid was present in the greatest quantity (0.29 – 0.60%). GLC-MS showed that hexane extracts contained 92 substances, including a-linoleic acid, ethyl esters of palmitic, palmitoleic, 13-methyltetradecanoic, and phenylacetic acids, phytol, diethylacetal isovaleraldehyde, hexahydrofarnesyl acetone, diethoxyethane, 14-methyl-8-hexadecenal, succinic acid diethyl ester, dihydrocitronellol, phenylacetaldehyde, and others.