The article is devoted to investigate the changes in the composition of biologically active substances (essential oils, lipid fraction, phenolic compounds) of the aerial part of the Bupleurum scorzonerifolium Willd. in depending on the phase of plant development. The greatest variety of compounds included in the composition of essential oils is characterized by a flowering phase. Fifteen terpene compounds – p-cymol, β-myrcene, trans-β-ocymene, limonene, (E,E)-α-farnesene, α-copaene, β-elemene, humulene, germacrene D, caryophyllene, γ-muurolene, bicyclogermacrene, Δ-cadinene, t-muurolol, spatulenol – are constant components of essential oils, regardless of phenophase. The quantitative content of these components varies from trace to major at different phenological phases. The coincidence of the main components of the lipid fraction was established. The main saturated acid is 16:0. Its content changes depending on the phase of vegetation – it is approximately at the same level determined in the phases of vegetation and flowering phases (26.78% and 27.26%, respectively) and there is a decrease in the fruit phase (18.17%). The main monounsaturated fatty acid is 18:1n9. Its greatest content was found in the fruiting phase, the smallest – flowering. The predominant polyunsaturated fatty acid is 18:2n9,12. Its greatest content was found in the vegetation phase (26.78%), the lowest - flowering (24.23%). However, the total content of unsaturated fatty acids exceeds the total content of saturated fatty acids in all phases of plant development. Although, their ratio varies from phenophase. There is a general pattern of highest content of phenolic compounds in the flowering phase for all studied samples. It was shown that during the flowering phase, the maximum accumulation of essential oils, lipids and phenolic compounds is observed.