The influence of the structure, phase composition, textural and colloidal properties of magnetic iron oxides nanoparticles in the form of aqueous suspensions with a concentration of 0.001 and 0.01 mg/L on the growth, productivity of tomatoes and quality of its fruits during their foliar processing was shown. It was found that the maximum positive effect was observed during foliar treatment of tomato plants with aqueous suspensions of iron oxide samples with specific surface area (~52 and ~75 m2/g), two-level hierarchical structure, hydrodynamic diameters (~150 and ~180 nm) in stable aqueous suspensions (the absolute value of the ζ-potential is ≈ 30 mV).