Continuing an investigation of the ether-soluble fraction of a methanolic extract of the herb Equisetum arvense L., by preparative chromatography on a polyamide sorbent and dilution with water and watermethanol we have obtained phenolic acid fractions. In the form of their TMS derivatives the phenolic acids were analyzed by the GLC method on a Tsvet-4 chromatograph with a flame-ionization detector, using a column 300 × 0.3 cm with 5% of SE-30 on Chromaton N-AW-DMCS at 212°C with helium as the carrier gas. The acids were identified by the method of additives and by comparison of the retention times of the TMS derivatives with those of authentic samples. The predominating phenolic acid in Equisetum arvense is caffeic acid. Phenolic acids of the hydroxybenzoic type (p-hydroxybenzoic, vanillic, gallic) are present in small amounts. This is the first time that phenolic acids have been found in Equisetum arvense L.