Rice plays an important role in feeding half of 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 35–60 percent of the calories consumed by 2.7 billion people. According to the Intergovernmental Panel on Climate Change (IPCC), CO 2 concentration in the atmosphere is expected to reach 700 µM M -1 by the end of the 21st century. Various researches have shown that the response of rice to increasing CO 2 in the atmosphere depends on the used cultivar and supply of nitrogen fertilizer. Therefore, the first experiment of this study evaluated the responses of 28 rice genotypes belonging to three varietal groups (local and improved genotypes from north and genotypes from the center of Iran) to two levels of nitrogen (2.85 and 1.42 mM N- ammonium nitrate in Yoshida’s nutrient solution). Treatments were arranged as factorial experiment in a completely randomized design. The results showed that tiller numbers, leaf area, SPAD index, shoot and root dry weight, plant total dry weight, plant height, and root length were significantly affected by genotype, N concentration and the interaction between genotype and N concentration. Considerable variation was observed among genotypes in response to the reduced N concentration in the nutrient solution. َAmong improved genotypes from north, Fajr and Khazar had the highest and Nemat and Shirudi had the lowest nitrogen use efficiency (NUE). While, among local genotypes from north, the highest NUE belonged to Hassani and Kazemi and the lowest NUE belonged to Tarom-Mantaghe and Ahlami-Tarom cultivars. Also, the highest and lowest NUE were achieved for Line 2- Firozan and Zayanderood among genotypes that are cultivated in the center of Iran. In the second experiment, the responses of four rice genotypes (Shirudi, Fajr, TaromMantaghe and Hasseni, chosen based on the results of the first experiment) were investigated to four levels of nitrogen (0.712, 1.42, 2.85, 3.79 mM of ammonium nitrate in the Yoshida nutrient solution) and two levels of air carbon dioxide (ambient; 360±50 µM and enriched; 700±50 µM). In the second experiment, rice plants were harvested at two different stages. The first harvest was done 30 days after treatments were imposed. Increasing CO 2 concentration increased chlorophyll content, leaf area and the root/ total plant dry weight ratio. The interaction effects of carbon dioxide and genotype were significant on shoot dry weight, chlorophyll and carotenoid content. Shoot dry weights of Shirudi, Hasseni and Fajr cultivars were increased and that of TaromMantaghe was decreased as a result of increased CO 2 concentration, although the increase in shoot dry weight was not statistically significant for Fajr genotype. In the second harvest, which was done 60 days after treatments were imposed, increasing CO 2 concentration decreased leaf area, the concentration and the content of nitrogen in shoots and increased nitrogen use efficiency and the concentration of nitrogen in roots which led to an increase in shoot: root nitrogen concentration. was significantly reduced in Shirudi and TaromMantaghe cultivars. The reduction in leaf area was only significant in Shirudi and TaromMantaghe. Increased CO 2 concentration increased chlorophyll content in Hasseni and Fajr but decreased chlorophyll content in Shirudi and TaromMantaghe cultivars. The highest nitrogen use efficiency was achieved in Fajr cultivar. Shoot dry weight was not significantly affected by increasing CO 2 concentration in the second harvest. Shoot dry weight was positively correlated with the concentration of nitrogen but negatively correlated with nitrogen use efficiency. The genetic diversity observed among rice cultivars in response to nitrogen and carbon dioxide can be used in breeding programs in order to improve productivity of agricultural systems under climate change effects.