Postharvest diseases significantly reduce the quantity and quality of the fruit crop. Its causes the loss of more than half of the agricultural production of fruits and vegetables. Therefore, this study aimed to find safe and environmentally friendly alternative fungicides to induce resistance against postharvest disease by inducing the natural resistance of fruits and vegetables by increasing the antioxidant enzymes that minimize the disease and enhance the quality of fruits and prolong the storage period. The following fungus is the most important pathogen of orange fruits after harvest (Penicillium digitatum). This study showed that the salicylic acid (SA), at 14 mM, inhibited the growth of mycelium with a percentage of 100 compared to the untreated control, while the percentage of inhibition of spore germination was 90.8%, compared to the untreated control. Moreover, SA inhibited the development of treated orange fruit rots by 39.06% and enhanced the enzyme peroxidase (POD), Polyphenoloxidase (PPO), and total phenols contents. We recommend the use of salicylic acid to reduce the severity of infection caused by P. digitatum that affects orange fruit.