Superoxide dismutase (SOD) activity in the leaves of transgenic tobacco plants with betaine aldehyde dehydrogenase (BADH) gene was about 36% higher than that in the control plants (parent plants), activities of per-oxidase (POD) and catalase (Cat) increased by about 62% and 88% respectively. Activities of ascorbate peroxidase (AsSPOD), dehydroascorbate redutase (DAsAR) and glu-tathione reductase (GR) in ascorbate-glutothion pathway located at chloroplasts increased by 67.7%, 47.9% and 38.8% respectively. These results indicated that the H2O2 produced by SOD catalyzing superoxide anion radicals (O2-) could be fully decomposed, and could not derive to form the strongest toxicant radicals · OH. This is the first report to elucidate quantitatively that the activities of two kinds of antioxidative enzymes decomposed radicals and active oxygen were matched. Photoinhibition tolerant capacity of the transgenic tobacco plants was 35% higher than that in the parent plants. Increment of photoinhibition tolerant ca Superoxide dismutase (SOD) activity in the leaves of transgenic tobacco plants with betaine aldehyde dehydrogenase (BADH) gene was about 36% higher than that in the control plants (parent plants), activities of peroxidase (POD) and catalase (Cat) Activities of ascorbate peroxidase (AsSPOD), dehydroascorbate redutase (DAsAR) and glu-tathione reductase (GR) in ascorbate-glutathion pathway located at chloroplasts increased by 67.7%, 47.9% and 38.8% . These results indicated that the H2O2 produced by SOD catalyzed superoxide anion radicals (O2-) could be fully decomposed, and could not derive to form the strongest toxicant radicals .OH. This is the first report to elucidate quantitatively that the activities of two kinds of antioxidative enzyme decomposed radicals and active oxygen were matched. Photoinhibition tolerant capacity of the transgenic tobacco plants was 35% higher than that in the parent plants. Increment of photoinh ibition tolerant ca