Rice plays an important role in feeding of half the world's population, most of which are living in developing countries, including Iran. This crop occupies one third of the agricultural lands dedicated to cereal production and provides 35 to 60 percent of the calories consumed by 2.7 billion people. On the other hand, salinity is one of the major agricultural problems in Iran and it is nessasary to pay more attention to crop improvement and management under saline conditions. Morovere, the concentration of carbon dioxide in the atmosphere has already reached 381 µM M-1 and is expected to rise up to 700 µM M-1 by the year 2100. Therefore, this study was conducted in two separate experiments under greenhouse condition at College of Agriculture, Isfahan University of Technology in 2013 in order to evaluate the responses of local and improved Iranian rice cultivars to salinity and also to increased level of carbon dioxide. In the first experiment, 27 rice cultivars (including three genetically grou local and improved cultivars from north and cultivars from center of Iran) were evaluated under two levels of salinity (0 and 100 mM NaCl in Yoshida’s nutrient solution). In the second experiment, four rice cultivars with different salt sensitivity (Neda, Deylamani, Shirodi and Domsorkh) were studied under four levels of salinity (0, 30, 60, 90 mM NaCl in Yoshida nutrient solution) and two levels of ambient (360±50 µM) and enriched (700±50 µM) carbon dioxide. In both experiments, treatments were arranged as factorial in a completely randomized design with three replications. In the first experiment leaf area, root length, root volume and total plant dry weight were significantly reduced under 100 mM NaCl salinity and the extent of reductions were different among tested cultivars. On average, total plant dry weight of local and improved cultivars from north and cultivars from center of Iran were 0.94, 1.09 and 1.38 gr/plant and reduced by 45, 49 and 57 percent under saline condition. Based on the reductions in total plant dry weight due to salinity, among local cultivars from north Deylamani and Domsorkh and among improved cultivars from north Neda and Shirodi were the most tolerant and sensitive cultivars, repectively. Among cultivars from center of Iran, Juzan was more salt tolerant than Zayanderood and Sazandegi. In the second experiment in which plants were harvested at two growth stages (21 and 42 days after treatments), plant height, root length, leaf area, shoot dry weight and the concentration of potassium in shoot and roots were decreased while the concentration of proline, malon-dialdehyde, sodium and the ratio of sodium to potassium in shoot and roots were increased under salt stress. Salinity decreased or increased the concentration of chlorophyll, carotenoids and soluble carbohydrates, depending on cultivar, salt and carbon dioxide levels. The extent of reductions in plant dry weight was greater at first than at second harvest. Plant dry weight of all four rice cultivars were increased under enriched level of carbon dioxide at the first harvest and the increase was highest in Neda. Howevere, this increase was only observed in cultivars Neda and Deylamani at the second harvest. Increasing level of carbon dioxide alleviated the negative effects of salinity on shoot dry weight of Shirodi but not other cultivars. The results of the this experiment showed that the effect of increasing level of carbon dioxide on growth and response of rice plants is dependent on salinity level, used cultivar and plant growth stage. Key words : Rice Cultivars, Salt stress, CO 2 enrichment, Proline, Soluble carbohydrates, Malon-dialdehyde, Sodium, Potassium.