Effects of exogenous nitric oxide (NO) on growth and changes in some physiological characteristics of perennial ryegrass seedlings under salt stress were investigated. The results indicated that exogenous NO donor, named sodium nitroprusside (SNP), at concentrations of 50-200 mol L-1 obviously alleviated the inhibition of salt upon the ryegrass seedling growth in comparison with the control; and 100 mol L-1 SNP had the strongest effects. Furthermore, treatments of the seedlings with SNP resulted in the pronounced alleviation in the increases of relative electrolyte leakage, K+ to Na+ ratio, the content of malondialdehyde and levels of reactive oxygen species in leaves under salt stress compared with the control. In addition, SNP treatments markedly enhanced the proline content and the activities of the main antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase and peroxidase in leaves of the seedlings under salt stress. These findings suggest that NO may alleviate the damage caused by salt in ryegrass seedlings via decreasing the Na+ content, increasing the contents of K+ and proline, and activating the antioxidant protest enzymes, thus improves salt resistance of the perennial ryegrass plants.