This study was conducted to evaluate the effects of different exogenous kinetin concentrations (10, 20, 30, 40, 50, and 60 µM) on plant growth and morphological damage in cucumber seedlings (Cucumis sativus L. cv. 'BT Bursalfa') under salinity stress. The experiment was carried out in a hydroponic system under controlled growth chamber conditions at Van Yuzuncu Yıl University, Faculty of Agriculture, Physiology Laboratory. Cucumber seedlings were subjected to 50 mM NaCl-induced salt stress and subsequently treated with various kinetin concentrations. Control plants were grown under optimal conditions without stress and hormone treatments. Total plant fresh weight, root length, root fresh weight, shoot fresh weight, leaf fresh weight, leaf number, plant height, shoot diameter, and internode distance were measured. Morphological damage was evaluated using a 1–5 visual scale. Data were analyzed using one-way ANOVA and Duncan's multiple range test (p<0.05). Results indicated that 50 mM NaCl salinity stress significantly reduced plant growth parameters and induced visual damage symptoms. Among kinetin treatments, 20 µM showed the most effective improvement in growth traits, enhancing root development and biomass accumulation under stress. Conversely, suboptimal (10 µM) and particularly supraoptimal (30–60 µM) kinetin concentrations inhibited plant growth, exacerbated morphological damage, and led to extreme phytotoxicity at 60 µM. These findings highlight the importance of optimal kinetin dosage under salinity stress conditions and demonstrate a clear biphasic (hormetic) dose-response relationship of exogenous cytokinin in cucumber seedlings.