Abstract. The aim of the study was to determine the content of the main groups of biologically active substances in the green mass of 8 species of perennial onions (Allium L.) during flowering. Methods. The freshly collected raw materials – leaves and flower scapes in A. altaicum Pall., A. flavum L., A. nutans L., A. obliquum L., A. ramosum L., A. schoenoprasum L., A. senescens L. var. glaucum Regel and A. strictum Schrader were analyzed. We used the generally accepted methods of phytochemical analysis. The dry matter content was determined by drying 1 g of raw materials at 100–105 °C to constant weight. The amount of phenolic compounds, pectin substances, total sugars, and carotenoids was determined spectrophotometrically. The amount of ascorbic acid was determined by the titrimetric method. All biochemical indicators, except for ascorbic acid, were calculated on the absolutely dry weight. Results. It has been established that the green mass of onions during flowering phase contains: dry matter – up to 28.3 %, flavonols – up to 1.8 %, tannins – up to 6.3 %, pectin substances – up to 14.7 %, total sugars – up to 42.9 %, ascorbic acid – up to 105.4 mg %, and carotenoids – up to 43.8 mg %. The content of catechins is 0.05–0.19 %. A. flavum and A. obliquum have the highest contents of main groups of biologically active substances, and the relatively low indicators are in A. ramosum and A. senescens var. glaucum. Scientific novelty. The quantitative content of catechins, tannins, pectin substances and carotenoids was studied in the onion species for the first time. The findings testify to the prospects of perennial onions as a source of various bioactive compounds.