Hydroponic experiments were carried out to study the effects of exogenous salicylic acid (SA, 0-2.0 mmol·L^-1) on the metabolic mechanism of proline in Jatropha curcas seedlings under salt stress (200 mmol·L^-1 NaCl). Seedlings of J. curcas under salt stress were treated with SA, and the content of proline, the activities of the key enzymes of proline metabolism as well as the expression of proline metabolismrelated genes in leaves of J. curcas seedlings were measured. The results showed that: (1) the exogenous SA (0.9 mmol·L^-1) treatment led to a significant accumulation of proline in J. curcas seedlings under salt stress. It also induced almost immediate and rapid increase of activities of the key enzymes Δ¹pyrroline5carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT) of proline biosynthesis, and upregulated JcP5CS and JcOAT expression. (2) SA decreased the activity of proline dehydrogenase (ProDH), a key enzyme of proline degradation, and inhibited JcProDH expression. (3) The SA treatment also increased tissue vitality, decreased the content of the lipid peroxidation product malondialdehyde (MDA), and alleviated electrolyte leakage in J. curcas seedlings under salt stress. These results showed that the SAinduced proline accumulation in the J. curcas seedlings under salt stress might be a combined result of the activation of glutamate and ornithine pathways of proline biosynthesis and the simultaneous inhibition of the proline degradation pathway. In addition, exogenous SA treatment can enhance salt tolerance in J. curcas seedlings, and proline might be a key factor in this increased salt tolerance.