The estimation of the protein content and amino acid composition under the influence of metal nanoparticles (Mn, Cu, Zn, Ag) for seven species of aquatic macrophytes: Limnobium laevigatum (Humb. & Bonpl.ExWilld.), Pistia stratiotes L., Salvinia natans L., Elodea canadensis Michx., Najas guadelupensis (Spreng.) Magnus, Vallisneria spiralis L. and Riccia fluitans L. was conducted. The plants were exposed during 7 days on the experimental solutions of metal nanoparticles at the rate of 1 g of plant per 100 ml of the mixture of stock colloidal solutions of metal nanoparticles (Mn - 0.75 mg/l, Cu - 0.37 mg/l, Zn - 0.44 mg/l, Ag+, Ag2O - 0.75 mg/l) diluted 200 times. In the five investigated species, reduction of the protein content was observed. However, this indicator remained stable only in P. stratiotes (52 g/ml) and, conversely, increased in V. spiralis (46 g/ml to 51 g/ml). The content of the studied amino acids in N. guadelupensis decreased by 46% (from 112.05 mol/g to 60.15 mol/g), in R. fluitans – by 44% (from 104.06 mol/g to 58.25 mol/g), in S. natans - by 23% (from 90.08 mol/g to 69.59 mol/g), in E. canadensis - by 10% (from 143.92 mol/g to 129.4 mol/g), and in P. stratiotes as well as in L. laevigatum - by 8% (from 210.65 mol /g to 193.77 mol/g and with 155.0 mol/g to 142.60 mol/g), but in V. spiralis, on the contrary, increased by 7% (from 91.31 mol/g to 97.59 mol/g). Changes in the composition and content of amino acids for each species of aquatic plant were analyzed. It was suggested that the studied plants, which belong to different families, have different defense mechanisms, according to which the amino acid composition of plants varies.