Callus cultures were obtained from the seeds of great burnet plants. Long-passed suspension cultures were obtained by transferring callus cultures to a liquid medium. The increase in the biomass of the suspension culture for the passage was 501%, the yield of dry biomass was 120 mg/g wet weight. The content of methanol-extracted phenolic compounds in the suspension culture increased during the passage and reached a maximum (34.6 mg/g dry weight) on the 22nd day of cultivation. An HPLC analysis of the phenolic compounds of the suspension culture and the rhizomes of the herbaceous plants was carried out. The proportion of some phenolic compounds in the obtained culture is significantly higher compared to their proportion in the rhizomes of plants. Such compounds were gallic, ferulic and caffeic acids, as well as condensed tannins. The obtained culture can be an object for conducting experiments on enhancing the synthesis of phenolic using various inductors. All this allows us to consider the obtained culture as a potential source of biologically active phenolic compounds.