Rising carbon dioxide concentrations in the atmosphere, elevated temperature and increasing the salinity of water and soil resources due to the reduction of rainfall are the major consequences of climate change in Iran. Under such conditions, adoption of proper management practices for application of nitrogen fertilizers as the most important nutrient element in plants becomes crucial. Furthermore, millets are important crops in thelanting patterdue to short growing season, and productivity under drought conditions. The present study was conducted to investigate the physiological, biochemical and growth responses of two millet cultivars (Bastan and Pishahang) under different irrigation water salinity (0 "control", 90 mM NaCl "salinity stress") and nitrogen nutrition levels (0 and 85 mg kg -1 , nitrogen from Urea fertilizer, N= 45%) as afactorial experiment arrangedin acompletely randomized design with three replications under two separate environments (ambient (390±50) and elevated air carbon dioxide concentrations (700±50 µmol mol -1 ) in 2016. Compared to the ambient CO 2 concentration, elevated levels significantly increased leaf area, concentrations of chlorophyll a (Chla), chlorophyll b (Chlb) and carotenoids (Car), root volume, shoot (N Shoot ) and root nitrogen concentration (N root ), root and shoot dry weights, but decreased proline concentration (Pro) and malondialdehyde (MDA) content. Salinity stress of 90 mM NaCl, compared to non-saline condition, increased Pro, protein content, MDA, sodium (Na + ), potassium (K + ), and calcium (Ca ++ ) concentrations in the root and shoot and N root , but decreased Chla, Chlb, Car, Fv/Fm, root volume, nitrogen concentration of shoot and root and shoot dry weights. N supply as compared with the no-treatment improved leaf area, Chla, Chlb, Car, Pro, protein content, root volum, N Root , N Shoot , root and shoot dry weights, but reduced Na + Shoot . Bastan indicated higher Chla (21%), Chlb (20%), Car (27%), Fv/Fm (5%), K + Root (14%), Ca ++ Root (22%), N Root (10%), Na + Shoot (16%), K + Shoot (13%), Ca ++ Shoot (34%) and N Shoot (17%) relative to Pishahang cultivar. While, Pishahang showed greater leaf area (14%), Pro (8%), MDA (15%), root volume (21%), root (11%) and shoot dry weights (19%) compared to Bastan cultivar. Salinity stress under ambient and elevated CO 2 , respectively, increased Pro (by 12% and 10%), Ca ++ Root (by 76% and 139%), N Root (by 15% and 23%), K + Shoot (by 34% and 55%) and Ca ++ Shoot (by 135 and 252%), but decreased Chla (by 39% and 4%), Chlb (by 15% and 2%), root volume (by 14% and 2.5%), root dry weight (by 66% and 15%) and shoot dry weight (by 25% and 9%). N supply increased leaf area by 14% and 86%, Chla by 30% and 42%, Chlb by 16% and 43%, root dry weight by 62 and 4% and shoot dry weight by 26% and 36% at the presence of CO 2 concentrations of 390 and 700, respectively. Both millet cultivarrespondedositively to elevated CO 2 , but Pishahang cultivar showed agreater[CO2]response. N supply under elevated CO 2 had a greater effect on shoot dry weight compared to ambient CO 2 concentration. Under ambient CO 2 , N supply increased root dry weight by 41% and 15% and shoot dry weight by 29 and 41% in Bastan and Bishahang cultivars, respectively. The highest shoot dry weight of 15.6 g plant -1 obtained under elevated CO 2 and 85 mg kg -1 N supply in Pishahang cultivar, and the lowest of 7.57 g plant -1 belonged to Bastan cultivar grown under ambient CO 2 and on-fertilizer N supply. It was concluded that the growth of millet is affected by the interaction of atmospheric carbon dioxide concentration with salinity and nitrogen condition, and elevated CO 2 is potent to modulate the destructive effects of salinity stress on the growth of this C 4 fodder crop. Keywords: Calcium concentration, Carbon dioxide, Climate change, Genetic diversity, Malondialdehyde content, Salinity stress