This work aimed to evaluate if chilling stress may be mitigated by elevated CO2 (EC) in Beta vulgaris L. plants. Photosynthetic rate was measured at 21% and 2% O2 after a short-term exposure of 5 h at four different treatments: 360 μmol(CO2) mol-1/25°C (AC); 360 μmol(CO2) mol-1/4°C (AC+LT); 700 μmol(CO2) mol-1/25°C (EC); 700 μmol(CO2) mol-1/4°C (EC+LT). Compared to AC+LT, EC+LT plants showed higher values of CO2 fixation, photochemical activity, and Rubisco amount. These latter invest a higher portion of photosynthetic electron flow to O2, differently from AC+LT plants that promote the regulated thermal dissipation processes. In EC+LT plants, the photosynthetic electron flow to O2 acts as a safety mechanism against the excess of absorbed light, upon return to prechilling conditions, allowing photosynthetic apparatus to maintain its efficiency. In AC+LT plants, the increase of thermal dissipation processes was not adequate to guarantee the PSII photoprotection and the photosynthetic recovery after chilling., C. Arena, L. Vitale., and Obsahuje bibliografii