Abstract: Salinity stress significantly harms the normal growth of turfgrasses and limits their wide establishment. This is especially so for Kentucky bluegrass, which is more sensitive to salinity than other turfgrasses. An experiment was carried out on two different cultivars of Kentucky bluegrass seedlings (‘Kenblue’ and ‘Midnight’) in order to explore the effect of 1 mmol/L exogenous spermidine (Spd) on the salt tolerance of the seedlings, which were cultured in a MS medium supplemented with 200 mmol/L NaCl. Under salinity stress, exogenous Spd alleviated both shoot and root growth inhibition and significantly increased the antioxidant activities of APX, CAT, POD, SOD and proline content. It also significantly decreased the membrane permeability and the content of H₂O₂, O2-· and MDA. Furthermore, exogenous Spd maintained ion balance by reducing Na⁺ content and increasing the contents of K⁺, Ca²⁺ and Mg²⁺, improving proper intracellular ion compartmentalization and stabilizing the membrane’s structure. We conclude that exogenous Spd can improve salt tolerance in the two cultivars of Kentucky bluegrass and provides a profitable approach for reducing the impact of salinity on widely planted turfgrasses.