The first action taken by plant to cope with salt stress is producing fast action substances, i.e., proline, malondialdehyde, peroxidase activity, etc, which produced during the first phase of stress as a temporary defence response against stress. Sensitive and tolerant sweet potato cultivars are different in response to salt stress. Four sweet potato cultivars (Xu-28, Xu-Zi-3, Xu-22 and Yan-Zi-3) were used in this study to identify the differences in response to salt stress between tolerant and sensitive cultivars. Seedlings were treated with 200 mM of NaCl and samples were collected at 0, 30 min., 1, 3, 6, 12, 24, 48 and 72-hours after treatment. A modified standard evaluation score (SES) of visual salt injury was used to measure the degree of salt tolerance after 14 days of salt stress treatment. SES results indicated that Yan-Zi-3 and Xu-22 were salt sensitive cultivars, while Xu-28 and Xu-Zi-3 were tolerant cultivars. During the first phase of salt stress exposure, the proline accumulation in leaves of the two tolerant cultivars (Xu-Zi-3 and Xu-28) was higher than in sensitive cultivars (Yan-Zi-3 and Xu-22). Malondialdehyde level started to increase at 30 minutes after salts stress treatment and it was higher in Xu-22 and Yan-Zi-3 (9.253 and 9.590 nmol/ml, respectively) than those recorded in Xu-28 and Xu-Zi-3 (4.368 and 4.466 nmol/ml, respectively). In addition, protein synthesis was more pronounced in tolerant than sensitive cultivars. Peroxidase responding to salt stress in sweet potato appeared at only one time point differed according to cultivars. Furthermore, the increment level in both of tolerant cultivars was higher than that of sensitive cultivars.