Abstract: By using FACE (FreeAir Controlled Environment)ozone system, a field plot experiment was conducted in 2008-2009 to study the effects of elevated ozone (O₃) concentration on the flag leaf microscopic structure, chlorophyll content, and grain weight of wheat. Two treatments were installed, i.e., ambient O₃ and 150% of ambient O₃, and four winter varieties, i.e., Yannong 19, Yangmai 16, Jiaxin 002, and Yangfumai 2, were taken as the test materials. At anthesis, elevated O₃ concentration had a slight damage to the flag leaf microscopic structure. The mesophyll cell and chloroplast structure began destroying, and the grana lamellae started breaking and loosing. Twenty-one days after anthesis, the differences in the leaf microscopic structure between the two treatments became significant. Under elevated O₃, the flag leaf senescence was accelerated, with the endomembrane system disintegrated, grana lamella disappeared, and corpus adiposum inside chloroplast broken down, resulting in a significant decrease of the chlorophyll content, photosynthesis rate, and grain  weight at maturing stage. Significant difference was observed among the test varieties in their responses to elevated O₃. Jiaxin 002 was tolerant, while Yangfumai 2 was sensitive to the ozone stress.