Panicum virgatumis considered a relatively cold-tolerant C4species to low night temperature from analysis of top growth, photosynthesis, dark respiration, and day–night fluctuation of nonstructural carbohydrate concentration in leaf blades grown under temperature regimes of 30–30, 30–20, and 30–10 °C. There was little influence of night temperature of 10 to 30 °C on top growth, although 20 °C night temperature was optimum. Plants grown under low night temperature (10 °C) showed a slightly reduced rate of photosynthesis early in the photoperiod, while plants at 30 °C night temperature had the highest rates of dark respiration. The time required for the plants to reach maximal photosynthetic rate from the beginning of the photoperiod was prolonged with decreased night temperature, being 1.0, 1.5, and 2.5 h for plants grown at 30–30, 30–20, and 30–10 °C regimes, respectively. Photosynthetic rates progressively declined during the rest of the photoperiod. The change in photosynthetic rate during the photoperiod and influence of night temperature on photosynthesis was highly correlated with the change in stomatal resistance to CO2transfer (r = −0.9). Starch and total sugars in leaves accumulated slightly with time after initiation of the photoperiod and then were reduced to low levels during the night at all temperatures. Night temperature had no effect on the accumulation of these nonstructural carbohydrates during the day or on depletion from the leaves during the night.