Application of silicon (Si) to soil is considered as an alternative approach to alleviate salinity stress in crop plants. Therefore, a field experiment was conducted to investigate the effects of Si application [control (without Si), 1.44 and 1.92 g.kg-1soil on membrane stability index (MSI), relative water content (RWC), leaf proline, soluble sugars, antioxidant activity, total phenols and dry matter accumulation of two sorghum (Sorghum bicolor) cultivars under three levels of salinity of irrigation water (5.2, 10.5 and 23.1 dS m-1). The results showed that leaf proline content, activities of ascorbate peroxidase (APX) and glutathione reductase (GR), Na+ concentration significantly increased only at high level of salinity, while, RWC and dry matter accumulation were significantly decreased at all salinity levels. Soil application of 1.44 g.kg-1 Si caused an increase in the activities of APX, catalase (CAT), superoxide dismutase (SOD), peroxidase (PRO), glutathione reductase (GR), total antioxidant and total phenol contents and 1.92 g.kg-1soil Si caused an increase in membrane stability index, soluble sugar and total phenol contents, CAT, SOD and total antioxidant activity. Soluble sugars, total phenols, SOD and total antioxidant activity and dry matter accumulation in cv. Omidbakhsh were higher than those in cv. Sepideh. In conclusion, alleviation of salinity stress by exogenous application of Si was found to be associated partly with enhanced antioxidant activity.

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