Effect of long-term salinity stress was studied in wheat, Karim (tolerant) and Om Rabiaa (moderately tolerant) under control and two levels of salinity (100 and 200 mM NaCl). Salinity stress decreased relative water content (RWC), chlorophyll (CHL), carotenoids (CAR), membrane stability index (MSI), and increased hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), proline, glycine-betaine (GB), soluble sugars, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) activity in both the genotypes and at all the stages. Salinity induced decrease in RWC, CHL, CAR, MSI, were significantly higher in Om Rabiaa than more tolerant Karim. Karim recorded higher activity of SOD, CAT, GR, as well as contents of proline, soluble sugar, GB and K, and comparatively lower H2O2 and TBARS contents compared with Om Rabiaa. Om Rabiaa also showed higher Na and Na/K ratio. Results show that salinity tolerance of Karim as manifested by lower decrease in biomass is associated with higher antioxidant activity, osmolyte concentration and potassium contents, and lower H2O2, TBARS and sodium contents than Om Rabiaa.