Relevance. The study of the effect of preparations containing amino acids on the accumulation of free amino acids in plants is relevant in assessing their regulatory and anti-stress effects.Methods. A laboratory experiment was carried out in 2020 on tomato plants of the Betta variety. Gray forest medium loamy soil was used as a substrate. The experiment was performed on soil with different salinity — a) control (the soil is not saline), b) saline soil (50 mmol/kg NaCl), c) saline soil (100 mmol/kg NaCl), using three feeding options: without top dressing, top dressing with “Sodium Glutamate”, top dressing with “Aminozol”. Amino acids were extracted from the roots and aboveground parts of plants in the vegetative growth phase with a mixture of “ethanol + chloroform + water” (12:5:2) and the method of high-performance liquid chromatography (HPLC) with pre-columnar derivatization of amino acids with phenylisothiocyanate was used. Results. Soil salinization with sodium chloride caused an increase in the amount of free amino acids in tomato seedlings. The total amino acid content increased to 849.8 µg/kg (50 mmol/kg NaCl) and 606.9 µg/kg (100 mmol/kg NaCl) compared to the control soil (385.3 µg/kg). Salinity contributed to the accumulation of serine (from 50.4 to 414.4 µg/kg) in seedlings. Treatment with preparations (“Monosodium glutamate” and “Aminozol”) affected the accumulation of a number of amino acids responsible for plant stress resistance. Supplementation with monosodium glutamate increased the total amino acid concentration to 1146.6 µg/kg (50 mmol/kg NaCl) and 1017.7 µg/kg (100 mmol/kg NaCl) compared to the corresponding variants without supplementation. At the same time, the content of glutamic (up to 188.3 and 425.1 µg/kg) and aspartic (up to 50.8 and 198.7 µg/kg) acids increased. “Aminosol” contributed to an increase in the amount of amino acids to 1834.2 µg/kg (50 mmol/kg NaCl) and 934.4 µg/kg (100 mmol/kg NaCl), respectively.