Increases in both atmospheric CO₂ concentration ([CO₂]) and temperature on the Earth's surface is likely to alter the photosynthetic responses of C4 plants. An experiment was conducted in sunlit, controlled environment chambers known as Soil-Plant-Atmosphere-Research (SPAR) units to determine if elevated [CO₂] and temperature interactively affect photosynthetic parameters of the C4 species, big bluestem. Ten treatments were comprised of two CO₂ levels of 360 (ambient) and 720 (elevated) mL L^-1 and five day/night temperature of 20/12, 25/17, 30/22, 35/27 and 40/32ºC. Treatments were imposed from 10 days after emergence (DAE) through 125 DAE. Plants grown in elevated [CO₂] had significantly higher leaf net photosynthetic rates (PN) and internal [CO₂] (Ci), but had lower conductance (gs) and transpiration rate (Tr) compared to that at ambient [CO₂]. At a given [CO₂], increase in temperature increased P_N and Tr. Plants grown at elevated [CO₂] did not differ for dark respiration (Rd), maximum quantum yield (F) and curvature (θ); had lower light compensation point (LCP); and higher maximum photosynthesis (Pmax) and light saturation estimate (LSE) than plants grown in ambient [CO₂]. The maximum rate of Rubisco activity (V_cmax), or light-saturated rate of electron transport (J_max) or triose phosphate utilization (TPU) were higher at elevated than at ambient [CO₂]. Increase in temperature increased Pmax, LCP, LSE, V_cmax, J_max and TPU , irrespective of the [CO₂].