The purpose of this study was to assess the antifungal properties of rosemary (Rosmarinus officinalis) extract and its generated silver nanoparticles (AgNPs) against pomegranate fruit-damaging fungi both in vitro and in vivo. Infected pomegranate fruits were collected from two orchards in the Taif region of Saudi Arabia. Fungal isolates were identified based on their morphological and molecular characteristics and found belonged to the genera Penicillium and Talaromyces. In vitro tests measuring the inhibition of mycelial growth on culture media and in vivo trials assessing symptom development on treated pomegranate fruits were used to evaluate the antifungal activity of different doses of rosemary extract and its AgNPs. According to the findings, AgNPs and rosemary extract demonstrated strong antifungal effects against the identified fungi. Nonetheless, the AgNPs exhibited better antifungal efficacy, exhibiting a significantly greater rate of mycelial growth inhibition and more successfully averting the development of disease signs on the fruits. AgNPs' increased activity can be ascribed to their vast surface area and small size, which improve their ability to interact with fungal cells and cause structural and functional disturbances. Overall, this study shows that rosemary extract and its silver nanoparticles have promising potential as natural, eco-friendly substitutes for synthetic chemical fungicides in the treatment of pomegranate post-harvest fungal diseases. This will help to improve fruit preservation and lower financial losses.