The cultivation of sorghum in Iran is recently becoming more important according to the climate change and water shortage crisis. Besides, it is necessary to investigate the effects of climate change factors such as increasing air CO 2 concentration and temperature on plant growth and yield. Under this conditions the proper management and improving the utilization efficiency of nitrogen fertilizers is important. Two pot experiments were therefore conducted in greenhouse to assess the effects of CO 2 concentration, temperature and nitrogen supply on the growth, dry matter partitioning and some physiological traits of IUA 3 sorghum line. Both experiments were carried out based on completely randomized design with three replications. In the first experiment, treatments were included four levels of nitrogen (0, 50, 100 and 150 mg kg -1 from ammonium nitrate source, N=34.4%) and two temperature regimes; ambient (25 ± 3°C) and elevated (35 ± 3°C) temperature. The results showed that increasing temperature decreased leaf stomatal conductance (0.14%), plant leaf area (19.5%), chlorophyll a concentration (4.26%), chlorophyll b concentration (31.1%), carotenoid concentration (8.03%), leaf protein concentration (2.85%), root dry weight (29.9%), shoot dry weight (27.0%), nitrogen use efficiency of root (5.08%) and shoot (20.9%), but increased shoot (16.7%) and root (5.18%) nitrogen concentration. The effect of increased temperature on stomatal conductance and leaf protein concentration was dependent on the level of applied nitrogen. Elevated temperature led to 3.43 (40%) and 17.0 mmol m -2 s -1 (63%) decreases in leaf stomatal conductance at 0 and 100 mg kg -1 N, respectively. However, at 50 and 150 mg kg -1 N leaf stomatal conductance was increased 11.1 (100%) and 10.2 mmol m -2 s -1 (115%). Leaf protein concentration was increased at elevated temperature by 0.009 g‌ kg -1 (9.28%) under 50 mg kg -1 N but decreased by 0.018 g ‌kg -1 (16.8%) at 100 mg kg -1 N. Elevated temperature had no significant effect on leaf protein concentration under 0 and 150 mg kg -1 N treatment. Nitrogen supply reduced the negative effects of elevated temperature on the root dry weight. Elevated temperature decreased root dry weight 0.957g (64%), 0.620 g (17%), 0.86 g (21%) and 0.52 (14%) at 0, 50, 100 and 150 mg kg -1 N, respectively. The positive effect of nitrogen fertilizer on shoot growth was higher at elevated than at ambient temperature. Under this experimental condition, the maximum shoot dry matter was obtained with application of 100 mg kg -1 N at ambient temperature but with supply of 150 mg kg -1 N at elevated temperature. In the second experiment, plants were evaluated at four levels of nitrogen (0, 50, 100 and 150 mg kg -1 ), two air carbon dioxide concentrations (ambient CO 2 of 390 ± 50 µmol mol -1 and enriched CO 2 of 700 ± 50 µmol mol -1 ) and two air temperatures (ambient temperature of 25 ± 3°C and elevated temperature of 35 ± 3°C). The results showed that the effect of elevated temperature on root growth was dependent on the air CO 2 concentration. Increasing temperature decreased root dry weight under enriched CO 2 concentration but increased it under ambient CO 2 condition. Carbon dioxide enrichment increased root (6.96%, insignificant) and shoot (27.0 %) dry weight. Elevated CO 2 concentration decreased the mean ratio of shoot/total biomass under all applied N treatments but increased it when no N was added to the soil. In conclusion, these results suggest that the amount of nitrogen fertilizer to gain high biomass production in sorghum depends on air carbon dioxide concentration and temperature. These findings are potent to benefit breeding programs and the management strategies for mitigating the influence of climate change on sorghum production. Key words : Assimilate partitioning, air carbon dioxide, climate change, high temperature, sorghum, nitrogen use efficiency.