Abstract: Immersing-treatment of Na2SO3. solution on spinach leaves affected the activity of superoxide dismutase in the leaves, lower concentrations (0.1, 1, 10 PPm) of the solution increased the activity and 100 PPm decreased the activity. The activity of glycolate oxidase, a key enzyme of Photo-respiration showed similar results. The relationship between activity changes of glycolate oxidase and the resistance of Plants treated by SO3 is dicussed.