We have studied the production of phenylpyruvic acid by mild stereospecific oxidation of D-phenylalanine (from D/L racemic mixtures) catalyzed by D-amino acid oxidase (DAAO) from Trigonopsis variabilis. The performance of this reaction requires the continuous bubbling of oxygen that inactivated soluble DAAO. The immobilization of the enzyme inside porous supports avoids the interaction of the enzyme with the hydrophobic oxygen/water interfaces; therefore, this inactivation cause is fully prevented Hydrogen per-oxide la reaction by-product) exerts deleterious effects on both the enzyme and the desired product (phenylpyruvic acid). These deleterious effects could be reduced by using immobilized DAAO and separately immobilized catalase; however, a much more effective elimination of hydrogen peroxide was achieved when both enzymes were coimmobilized. The effectiveness of coimmobilized catalase in preventing phenylpyruvic destruction by hydrogen peroxide is more than 20-fold higher than that of separately immobilized catalase. In fact, by using DAAO/catalase-coimmobilized derivatives, more than 98% phenylpyruvic acid was obtained after complete oxidation of D-phenylalanine by using the racemic mixture as substrate. This also prevented enzyme from inactivation. In this way, 40 reaction cycles were performed without apparent loss of enzyme activity. These results open an effective and simple way of using any oxidase where we can expect very similar problems to those described in this paper