The beneficial effects of elevated CO 2 on plants are expected to be compromised by the negative effects posed by other global changes. However, little is known about ozone (O 3)-induced modulation of elevated CO 2 response in plants with differential sensitivity to O 3. An old ( Triticum aestivum cv. Beijing 6, O 3 tolerant) and a modern ( T. aestivum cv. Zhongmai 9, O 3 sensitive) winter wheat cultivar were exposed to elevated CO 2 (714 ppm) and/or O 3 (72 ppb, for 7h d –1) in open-topped chambers for 21 d. Plant responses to treatments were assessed by visible leaf symptoms, simultaneous measurements of gas exchange and chlorophyll a fluorescence, in vivo biochemical properties, and growth. It was found that elevated CO 2 resulted in higher growth stimulation in the modern cultivar attributed to a higher energy capture and electron transport rate compared with the old cultivar. Exposure to O 3 caused a greater growth reduction in the modern cultivar due to higher O 3 uptake and a greater loss of photosystem II efficiency (mature leaf) and mesophyll cell activity (young leaf) than in the old cultivar. Elevated CO 2 completely protected both cultivars against the deleterious effects of O 3 under elevated CO 2 and O 3. The modern cultivar showed a greater relative loss of elevated CO 2-induced growth stimulation due to higher O 3 uptake and greater O 3-induced photoinhibition than the old cultivar at elevated CO 2 and O 3. Our findings suggest that the elevated CO 2-induced growth stimulation in the modern cultivar attributed to higher energy capture and electron transport rate can be compromised by its higher O 3 uptake and greater O 3-induced photoinhibition under elevated CO 2 and O 3 exposure.