The most of plant secondary metabolites protect plants against pathogens. Polyphenols and their derivatives play an important role in protection of plants against the fungal diseases. We studied the Rheum rhaponticum L. (Polygonaceae) alcoholic extract in order to reveal the anthraquinone derivatives which induce resistance to plant phytopathogens and act as an antimicrobial agent with fungicidal activity. An alcoholic extract of Rheum rhaponticum L. was prepared and analyzed using chromatography.