Fusarium solani (F. solani) and Alternaria solani (A. solani) are among the most destructive pathogenic fungi affecting potatoes, causing significant crop losses in both field and post-harvest conditions. Current control relies heavily on synthetic fungicides which pose serious environmental and health risks. Therefore, there is a growing need to find efficient and environmentally friendly alternatives to combat fungal infections in potatoes. This study offers chitosan (CS) and zinc oxide (ZnO) nanoparticles (NPs) as potential fungicides against A. solani and F. solani. We evaluated their antifungal properties and elucidated the mechanism underlining their activity. Our results revealed that both CS and ZnO NPs exhibited pronounced antifungal activity against the two pathogenic strains by effectively inhibiting the mycelium growth. Furthermore, we discovered that the activity of the NPs involved the induction of oxidative stress in fungal cells and changes in the molecular organization of their membranes.