Guava cultivation in the Brazilian semi-arid region is constrained by the scarcity of high-quality water, which necessitates the use of saline water for irrigation. In this context, the application of antioxidant substances, such as ascorbic acid (AsA), has emerged as a promising strategy to mitigate the deleterious effects of salt stress. This study aimed to evaluate the effects of foliar AsA application on the morphophysiology of guava plants in the post-grafting phase when irrigated with saline water. The experiment tested five levels of water electrical conductivity-ECw (0.9, 1.5, 2.1, 2.7, and 3.3 dS m-1) and four concentrations of AsA (0, 200, 400, and 600 mg L-1). Salt stress, induced by water with conductivity from 0.9 dS m-1 onwards, adversely affected gas exchange, photosynthetic pigments, and growth parameters of the guava plants. Conversely, foliar application of AsA demonstrated beneficial effects both as an isolated factor-improving relative water content and the CO2 assimilation rate-and through its interaction with salinity. The importance of this mitigating action was particularly evidenced by the significant interaction in attenuating chlorophyll a degradation and, most notably, in promoting vegetative vigor, even in plants subjected to the highest level of salt stress (3.3 dS m-1), at 150 days after transplanting. The 600 mg L-1 dosage of ascorbic acid (AsA) proved to be the most effective. The results indicate that foliar AsA application is a promising tool for managing salt stress, as it contributes to improving the physiology and growth of guava trees.