Applying Si suggested as an alternative approach to alleviating salinity stress in crops. Therefore, a field experiment was conducted to investigate the effects of silicon application (control (without Si), 1.44 and 1.92 g.kg-1soil) on membrane stability index (MSI), relative water content (RWC), proline, soluble sugars, ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), peroxidase (PRO), glutathione reductase (GR), total antioxidant, total phenol, Na, K and dry matter of tow sorghum (Sorghum bicolor L.) cultivars (CV) under three levels of salt stress (5.2, 10.5 and 23.1 dS m-1). Leaf proline content, APX and GR activity and Na concentration significantly increased only at high levels of salinity, RWC and dry matter accumulation was significantly decreased with increasing salinity. Supplied 1.44 g.kg-1 soil Si cause increased activity of APX, CAT, SOD, PRO, GR, total antioxidant and total phenol concentration and 1.92 g.kg-1soil Si caused an increase in MSI, soluble sugar and total phenol concentration, CAT, SOD and total antioxidant activity. Soluble sugar, total phenol and K concentration, SOD and total antioxidant activity and dry matter accumulation in Omidbakhsh was higher than Sepideh. In conclusion, alleviation of salinity stress by supplying exogenous Si obtained in high levels of salinity by expression of antioxidant activity.

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