Nowadays many reports confirmed the effect of different nanoparticles (NPs) on the growth and secondary metabolite production in various microorganisms. Some of them, NPs like Ag, Au and oxides of Al, Ti, Si and Zn have harmful effect on the cells of microorganisms. Iron NPs are expected to be nontoxic, due to using Fe atom in several pathways of cell metabolism and, therefore, low iron toxicity. The use of iron NPs in technologies for remedying polluted environment was caused by their efficiency in reduction reactions, mobility, and high reactivity, due to the high surface area. The present study aims to determine the effect of magnetite (Fe3O4), zero-valent iron Fe(0) NPs, and fluorinated dinitroaniline herbicide trifluralin on growth of mycelial fungi. Fungal strains were isolated from soil long-term polluted with obsolete pesticides, DDT and trifluralin. The inhibition activity of iron NPs and trifluralin was evaluated using express-method. Each fungal strain had an individual reaction to the solutions of iron nanoparticles. At the same time, Fe(0) NPs, as well as magnetite NPs, had a stimulating effect on the formation and maturation of spores of micromycetes. Addition of trifluralin to the culture medium had a growth inhibition effect on micromycetes, but this effect was reduced, when trifluralin was mixed and incubated with iron NPs for 1 hour before.