Food and pharmacological value in onion leaves is mainly represented by ascorbic acid, chlorophylls and secondary metabolites: carotenoids, phenolic compounds. At the same time, their quantity depends on the conditions of cultivation and treatment with biostimulants. The experiment was carried out in a greenhouse on sod-podzolic soil in the Moscow region under conditions of natural insolation at a temperature of 20 ... 25 ° C in March using varieties of VNIISSOK selection – Chernyj princ and Zolotnichok. The effect of Albit and Amir biostimulants on the content of antioxidants and photosynthetic pigments in the leaves of onion was studied. The work shows the promise of using growth-stimulating plant and bacterial preparations for foliar treatment of onion leaves, which allow increasing the yield of leaves and the content of antioxidants. In the leaves of the Chernyj princ variety, an increase in the content of ascorbic acid by 30% was observed when treated with biostimulant Amir, as well as an increase in leaf weight by 8% when treated with Amir and by 14% when treated with biostimulant Albit. Foliar treatment of onion leaves with biostimulants Albit and Amir resulted in an increase in the amount of ethanol-soluble antioxidants.