Nanoparticles are implemented in different biotechnological fields, and there is interest in their use in plant biology. Nanotechnology can help overcome the persistent limitations of using conventional fungicides in the management of plant diseases, contributing to a safer environment. Hence, this study is focused on evaluating the behavior of nanoparticles on two different strains of Fusarium oxysporum, which have a wide-ranging occurrence in tomato production and account for important economic losses. Fusarium oxysporum is an ascomycetous fungus that is well-known as a soilborne plant pathogen, adapted to any soil type, and it lives in different forms on organic materials. Gold–chitosan and carbon nanoparticles were suspended in potato dextrose agar growth media, and their antifungal activity was evaluated at 1, 3, 5, and 7 days after incubation by measuring the diameter of fungal colonies. The results showed that the nanoparticles have antifungal properties against F. oxysporum, the fungal colony growth diameter being reduced. Likewise, it was observed that the colony diameter was smaller when the nanoparticle concentration increased. However, in the case of one F. oxysporum strain, the highest nanoparticle concentration applied during the experiment’s execution was not able to completely inhibit fungal growth.