Nanoparticles now have found wide use in all sectors of the economy. Successful use in pharmacology are (obtaining various drugs), medicine (treating different diseases), biology (immune research in the study of intracellular processes, etc.), technologies (electronics, information technology etc.) in production, processing and preserving food. In food production, nanoparticles allow the administration of vitamins and minerals with food, intensifying flavors and removal of pathogens in food. Agriculture uses more efficient spreading of pesticides and fertilizers and water decontamination [1-4]. Based on the above mentioned, the research aim was to study the action of Fe3O4 nanoparticles on growth of micromycetes. As a subject of researchserved 8 strains of micromycetes from NCNM and 9 strains isolates from infected soil with persistent organic pollutants. As pollutant was studied trifluralin. Were used Fe3O4 nanoparticles with size 17-20 nm. It was studied the growth of fungal strains in liquid and agarized medium Czapek supplemented with different doses of nanoparticles in the presence of trifluralin. To find the action of nanoparticles on micromycetes capable to growing in the presence of trifluralin, the isolates were grown on agar Czapek medium without glucose + 500mg/l trifluralin supplemented with different doses of nanoparticles of iron: 1.0; 10.0; 25.0; 50.0, and 100.0 mg/l. The results showed that, of the 8 strains grown on Czapek medium without glucose 500 ml trifluralin in the presence of various concentrations of nanoparticles of Fe, 2 did not growth, at 3 strains increase was the same as on the medium with trifluralin and 3 strains has been a stimulus to growth. These are strains Sp.11; Sp.5; and Sp.15. Sp.11 strain does not grow on Czapek medium without glucose, but growth on the medium Czapek + 500 mg/l trifluralin. Supplemented of Czapek medium + 500 mg/l trifluralin with nanoparticle concentration of 1 - 10 mg/l, stimulates the growth of this strain, but increase their dose up to 50-100 mg/l lead to stopping the increase. Sp.5 and Sp.15 strains growth well both on Czapek medium without glucose and supplemented medium with trifluralin. In this case the action of trifluralin was neutral and in the presence of nanoparticles in a concentration of 10-25 mg/l and Sp.15 Sp.5 strains showed growth stimulation. The results obtained from submerged cultivation of strains Sp.5; Sp.15 and Sp.11 not confirm exactly the same data obtained on agar medium. Thus, on the liquid medium only strain Sp.5 demonstrates stimulating accumulation of biomass from 33.3 to 66.6%, compared to control by usingconcentration of nanoparticle 1 - 25 mg/l. 166.6% maximum biomass accumulation was obtained after using the minimum concentrations of the nanoparticles of 1 mg/l. Sp.15 strain and Sp.11 in the case shown the same results as on agarized medium. Strain Sp. 15, the biomass accumulated to the use of nanoparticles in a concentration of 1 mg/l, is only 25 % at a concentration of 10 - 25 mg/l - 100%, and increasing the concentration up to 50-100 mg/l biomass accumulation up to 50 % diminish control variant. In case of strain Sp. 11 at all concentrations of nanoparticles tested have registered a significant decrease in biomass accumulation. In embodiments the nanoparticle concentration 1mg/l; 50 mg/l and 100 mg/l, accumulated biomass was 37.5% and the variations of concentrations of 25 mg/l and 50 mg/l - 50% compared to the control. The obtained results demonstrate that the action of nanoparticles on micromycetes is different depending on their concentration and cultivation methods. Thus in the case of immobilization of the nanoparticles on the surface of the submerged cultivation micromycetes, and their entry into cells it is more accessible, more intense, and in some cases the cell wall destruction takes place causing their death. Of soil polluted with trifluralin were isolated and selected nine strains. Selected strains were inoculated on Czapek non-glucose solid medium supplemented with trifluralin at a concentration of 300 and 500 mg/l in the presence of nanoparticles (1; 10; 25; 50; 100 mg/l). The results showed that the only one of nine strains did not grow on mentioned media. On medium Czapek without glucose 4 strains grow well, and 4 weaker. Growing submerged in nutrient medium with trifluralin showed diminishing growth to 2 strains (Sp.3 and Sp.5) and increasing strain Sp.2 greatly on trifluralin with concentration of 500 mg/l. The presence of Fe nanoparticles in media supplemented with trifluralin showed an increase in growth to 3 strains, Sp.3; Sp.5 and Sp.9. Thus Sp.3 and Sp. 5 strain grows well on Czapek medium without glucose and nutrient supplementation of medium with trifluralin concentration of 300 or 500 is increased diminish, but in the presence of nanoparticles growth increases again. This increase in growth was manifest at strain Sp.3 with use of nanoparticle in concentration 10; 25 and 50 mg/l. The same was registered on strain Sp.5, regularity and increasing growth under the influence of nanoparticles of Fe in medium Czapek + 300 mg/l trifluralin concentration of 1-25 mg/l and the medium Czapek + 500 mg/l trifluralin concentration of 10 and 25 mg/l. A considerable increase in the presence of nanoparticle growth was registered strain Sp.9. This strain grows poorly on Czapek medium without glucose and supplemented medium with trifluralin, but the enhances growth on Czapk + 300 mg/l in the presence of nanoparticles in concentration of 1-25 mg/l and the medium Czapek + 500 mg/l concentration of 10-25 mg/l. The results showed that the nanoparticles can annihilate action of trifluralin on micromycetes, as well as stimulate growth. Thus, among the selected strains of soil polluted with trifluralin only Sp.9 strain exhibited growth stimulation in the presence of nanoparticles. According to the results we conclude that the action of Fe3O4 nanoparticles on micromycetes depends on the method of cultivation and their concentration. They can stimulate growth of micromycetes in the presence of trifluralin.