Active packages are those incorporated with additives such as antioxidants and antimicrobials, which interact directly with food and make it possible to increase its shelf life. This work aimed to develop an active film, elaborated from sodium alginate and chitosan, incorporated with nanoparticles of zinc oxide (ZnOnano) or sodium benzoate (SB), and to evaluate their in vitro antimicrobial potential on phytopathogenic fungi. To develop the composite film-forming solutions of alginate (2% m/v) and chitosan (1% m/v), and additionally, those solutions were crosslinked with calcium chloride at two different concentrations (0.375% or 0.5%). Then, the filmogenic solutions were mixed in a 9:1 ratio (alginate/chitosan). ZnOnano < 50 nm (0.5 mg/mL) or SB (30 mg/L) were added to the filmogenic solution, poured into Petri dishes, and dried in an air circulation oven at 40°C for 16h. Colletotrichum sp., Fusarium sp., and Penicillium sp. were isolated from papaya and orange fruits lesions, cultivated on Potato Dextrose Agar (PDA) medium and purified. The antifungal activity of the films was determined by the agar diffusion method. Spore suspensions (200 µL, 106 CFU/mL) were spread in a Petri dish containing a PDA culture medium. Discs of the films, 1.5 cm in diameter, were exposed to UV light for 5 min, and then deposited on the PDA medium surface. Plates were sealed and stored at 25°C in a BOD chamber for 2 days. Halo formation around the different developed films was evaluated after 48 hours of incubation. Three repetitions of each film were performed, consisting of 3 discs, arranged equidistant from each other. Films without antimicrobial agents were used as controls. The crosslinking factor of the films did not influence the antimicrobial activity against the non-crosslinked films. There was no inhibition halo formation on the films for the three evaluated fungi. However, it was possible to observe on the treatments with ZnOnano, regardless of crosslinking, remained intact and translucent, not observing any type of fungal growth on or under them. The films added with SB and the control film did not show antifungal action on the three tested fungi. Thus, it can be inferred that the effect of the nanocomposites was due to contact and not to diffusion in the medium. The fact that there was no diffusion of nanoparticles into the culture medium may be linked to some factors such as the affinity of the particles with the polymeric matrix, agglomeration of nanoparticles, or even the entrapment of nanoparticles in the compacted polymeric matrix. Fungi from the genera Colletotrichum sp., Fusarium sp., and Penicillium sp. are causal agents of various diseases and are of great importance in the postharvest of various fruits. The films developed containing ZnOnano, due to their antifungal effect, could be applied as postharvest active packaging, since they allow the inhibition of fungal growth by contact, and can minimize losses.