The development and investigation of metal oxide nanoparticles has attracted a lot of attention due to their useful applications in catalysis, energy storage, magnetic data storage, sensors, and ferrofluids [1]. Recently it was reported the possibility to obtain iron oxide nanoparticles from µ3-oxo trinuclear clusters as precursors [2]. The TG analysis data have shown that the mixed iron oxides are obtained through thermal decomposition processes at temperatures above 500 ºC. Fig. 1 TEM image of Fe2ZnO 4 nanoparticles In this work we report the study of the influence of Fe2O3, Fe2ZnO4 and Fe2CuO4 nanoparticles on the morphocultural and biosynthetic properties of micromycetes. The following phytopathogens were taken as test cultures for the performed experiments: Aspergillus niger, Alternaria alternata, Borytis cinerea, Fusarium solani, Fusarium oxysporum. At the cultivation of these submersed strains, in the Czapek medium supplemented with Fe2O3, Fe2ZnO4 and Fe2CuO4 nanoparticles, the accumulated biomass increased more significantly in the Fe2O3 and Fe2ZnO4 cases. In the presence of Fe2CuO4 nanoparticles, biomass stimulation was recorded in only 2 of the 5 studied Aspergillus strains, and in 3 strains a decrease in biomass accumulation ranging from 7-15% compared to the control was observed. Nanoparticles of Fe2O3, Fe2ZnO4, and Fe2CuO4 have been more beneficial for the growth and accumulation of biomass of strains belonging to the Penicillium genus. Treating phytopathogens with the obtained metabolites of the Trichoderma strains has demonstrated antifungal activity stimulation. The most significant stimulation of antifungal activity was in the case of Fe2ZnO4 nanoparticles. Thus, we can conclude that nanoparticles of Fe2O3, Fe2CuO4 and Fe2ZnO4 can alter the morphocultural and biosynthetic properties of micromycetes.