A method for isolating flavonoid Dihydroquercetin (taxifolin) from wood parts including lower portions of the trunk, referred to as butt logs, bark and roots. The method includes extracting either the particle-reduced chip fraction obtained by chipping or subdividing into chips the butt logs and roots, or dry cork fraction of the bark or powdered bark obtained as a residue in finishing of mechanical wood products with a polar solvent. The method further includes recovering the extract. The wood used in the method is a hardwood or a coniferous wood selected from wood of Larix genus, spruce wood of the genus Picea, fir wood of the genus Abies, pine wood of the genus Pinus, and wood of Pseudotsuga genus. The isolated prime substance from all of the above genus is a flavonoid such as Dihydroquercetin (taxifolin).