Environmental stresses including soil salinity are severely affecting rice growth and productivity. The triamine Spermidine (Spd), a member of Polyamines (PAs), a group of phytohormone-like natural amine compounds has been shown to play essential roles in salt stress tolerance in many important crop plants. The effects of exogenously supplied Spd were investigated in two rice cultivars differing in salt tolerance level to determine the roles of Spd on the modulation of physiological parameters related to salt-stress responses. Thirty day-old seedlings of two rice cultivars, Pokkali (salt-tolerant) and KDML 105 (salt-sensitive), grown in nutrient solution were exposed or not to 1 mM Spd for 24 h before submitted to salinized solution containing 150 mM NaCl for 7 days. Salinity stress resulted in significant reduction in plant height, fresh and dry weight of both cultivars but Spd pretreatment significantly increased these growth parameters only in Pokkali. Salt-stress induced considerable disturbance in several physiological processes inhibitory for growth including chlorophyll loss, accumulation of hydrogen peroxide and increase in lipid peroxidation, increased electrolyte leakage and increase in Na+/decrease in K+/Na+. Spd pretreatment led to the reversal of those inhibitory effects in both cultivars. This study showed that exogenous Spd can be applied as short-term pretreatment prior to introduction of salt stress to help elevate salt tolerance of rice and confirmed earlier observations that exogenous Spd offered protective roles on salinity-stressed rice by stabilizing membrane, scavenging free radicals and maintaining K+/Na+ status.