Salinity is one of the major environmental aspects, which affects on plant growth, development and productivity of the agricultural crops worldwide. The aim of this study was to evaluate germination, initial growth parameters, antioxidant enzyme (CAT, APX and GR) activities and proline accumulation, Na+ / K+ content in seedlings of four onion cultivars Agrifound Rose, Bellary, Prema-178 and Nasik Red exposed to salt stress with different concentrations of NaCl (0, 50, 100, 150 and 200 mM). In all cultivars, morphological parameters and relative water content decreased with increasing NaCl concentrations, whereas antioxidant enzyme activities, proline accumulation and Na+ / K+ content increased. Bellary cultivar showed highest salt tolerance than the Agrifound Rose, Prema-178 and Nasik Red. Decrease in RWC was least in Bellary as compared to other cultivars. The results suggest that high NaCl concentrations have a negative effect on the physiological quality of onion seedlings, resulting in lower seedling growth rates and increased antioxidant enzyme activity and among four cultivars Bellary was found more tolerant to salt stress.