The main objective of this work is to evaluate the nanoparticles of chitosan with tripolyphosphate and polyethylene glycol (ChNPs + TPP + PEG) in an in vitro model and in vivo against F. solani and to demonstrate by means of transmission electron microscopy (TEM) the interaction of these with the fungus and with the host cell. Two experimental models of nanoparticles were used and it was found that experimental model 2 (QNP2) presented a better antifungal effect in the in vitro test, and that is why these nanoparticles were evaluated in vivo in chonto tomato (Solanum lycopersicum) seedlings, determining an optimal application method for the nanoparticles of experimental model 2. The transmission electron microscopy allowed to demonstrate the interaction between the experimental model of nanoparticles 2 and the cell wall and membrane of the fungus, as well as to determine the interaction between this nanoparticle and the model vegetable. Concluding that the nanoparticles of experimental model 2 have an antifungal effect on the wall and membrane of the fungus and by their composition it is possible that they generate a systemic acquired resistance response in the plant generating defense mechanisms against the fungus.