Abstract: In this communieation we report the effects of malic and glyceric acids, serine, and glutamic acid on the activity of glycolate oxidase from the leaves of Brassica parachinensis Bailey. It was fonnd that malic acid, serine, and glutamic acia inhibited competitively the activity of glycolate oxidase;the Ki values for serine, malic acid, and glutamic acid were 5.5,7.0,and 13.5 m mol/L respectively,while the km (glycolate) of glycolaie oxidase was 0.36m mol/L determined by the Li-neweaver-Burk plots. Glyceric acid showed no marked effect on the activity of this enzyme. The significance of the regulation of glycolate oxidase by these acids in the photorespiratory glycolate pathway is discussed.