This investigation was carried out in two separate experiments in a geenhouse at Isfahan University of Technology, Iran in 2013. In the first experiment 17 barley genotypes were evaluated under two levels of carbon dioxide (380 and 700 µM) and two levels of salinity (0 and 150 mM NaCl in nutrient solution). The results showed that the responses of all tested barley genotypes to elevated CO 2 were positive in terms of dry matter accumulation, but to different extents. The positive effect of elevated CO 2 was low (less than 10% increase in dry matter accumulation) in Eram, Valfajr, A21, A51 medium (between 10 and 20%) in Gohar, Karoon, A5، A16، A24، A27، A42، A45، A52، A58، A61 A68 (more than 20%) in A57 genotype. There were considerable differences among barley genotypes in response to salinity. The extent of decrease in shoot dry weight due to salinity of 150 mM NaCl was less than 20% in A51, between 20 and 40% in Karoon, Eram, Valfajr, A16، A21، A24، A27، A42، A45، A52 ، A57، A58، A61، A68 and more than 40% in Gohar and A5. In the second experiment, in which plants were harvested at physiological maturity, salinity decreased the concentration of potassium in shoot and roots, K/Na ratio in shoot and roots, chlorophyll and carotenoid concentrations, plant height, leaf area, shoot and root dry weight but increased sodium concentratio in shoot and roots, proline concentration and the activities of catalase and ascobate peroxidase enzymes. Under increased level of air CO 2 , potassium concentrations in shoot and roots, K/Na ratio in shoot and roots, chlorophyll and carotenoids concentrations, plant height, leaf area, shoot and root dry weight, leaf area and the activities of catalase and ascobate peroxidase were increased but proline concentration and the concentration of sodium in shoot and roots were decreased. The extent of increases in the concentration of potassium in shoot and roots, chlorophyll concentration, plant height, leaf area, the activity of catalase and shoot and root dry matter at elevated CO 2 was greater under saline than under non-saline condition. While, the positive effect of elevated CO 2 on root volume, the activity of ascobate peroxidase and carotenoid concentration (only in the first experiment) was greater under non-saline condition. Regardless of salinity level and genotype, the positive effect of elevated CO 2 on plant growth was greater under elevated than under ambient temperature. At elevated compared to ambient temperature, the concentration of potassium in shoot and roots, plant height, chlorophyll concentration, leaf area, plant total dry weight were decreased, while, the concentrations of sodium in shoot and roots, proline concentration and the activities of catalase and ascobate peroxidase were increased. The results of this experiment showed that elevated concentration of air CO 2 positively affected the growth of tested barley genotypes and the extent of the these effects was dependent on genotype, temperature and salinity level. Keywords: Climete change, Barley genotypes, Salinity, Elevated CO 2, temperature, sodium, potassium, Anioxidant enzymes, carotenoids, proline.