Postharvest fungal infection is the common cause of fresh fruit losses. Thus, effective antifungal agents are highly required. Herein, copper-based metal–organic frameworks (MOFs) were used as a precursor for the synthesis of copper oxide (CuO) embedded into carbon (CuO@C). The materials' crystallinity was confirmed using X-ray diffraction. X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) approve the elemental species and concentration of copper in the synthesized materials. Transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and scanning electron microscopy (SEM) reveal the successful formation of CuO-embedded C, that is, CuO@C, with a particle size of 36–123 nm. CuO@C nanoparticles are used as an antifungal agent against four economic postharvest plant pathogens; Alternaria alternata (black spot disease of tomato), Fusarium oxysporum (rot disease of tomato), Penicillium digitatum (gray mold disease of lemon), and Rhizopus oryzae (soft rot disease of banana). The inhibition zones were 36 ± 0.5, 20.2 ± 0.4, 16 ± 0.5, and 10.2 ± 0.1 mm for R. oryzae, P. digitatum, F. oxysporum, and A. alternata, respectively. CuO@C antifungal action includes significant inhibition of cellulases and amylase enzyme activity, decreasing the potentiality of fungal pathogenicity and fruit disease. CuO@C exhibited high antifungal activity against postharvest antifungal species.