Biodiesel is an alternative to petroleum diesel fuel. It is a renewable, biodegradable, and nontoxic biofuel. Interest in the production of biodiesel from Jatropha curcas L. seeds has increased in recent years, but the ability of J. curcas to grow in salt-prone areas, such as the Caatinga semiarid region, has received considerably meager attention. The aim of this study was to identify the main physiological processes that can elucidate the pattern of responses of J. curcas irrigated with saline water, which commonly occurs in the semiarid Caatinga region. This study measured the activity of the antioxidant enzymes involved in the scavenging of reactive oxygen species, which include catalase (CAT) and ascorbate peroxidase (APX), as well as malondialdehyde (MDA) levels. The levels of chlorophyll (Chl), carotenoids, amino acids, proline, and soluble proteins were also analyzed. The net carbon assimilation rate (P N ), stomata conductance (g s ), and transpiration rate (E) decreased with salt stress. The activities of CAT and APX were decreased, while H 2 O 2 and MDA levels as well as electrolyte leakage were significantly increased in salt-stressed plants compared to the untreated ones. These observations suggest that the ability of J. curcas plants resist to salt stress is associated with the activities of protective enzymes and their defensive functions. However, our results indicate that the reactive oxygen species scavenging system is not sufficient to protect J. curcas leaves against oxidative damage caused by salt stress, and, therefore, it cannot be treated as a salt tolerant plant species.