D-amino acid oxidase (DAAO)from Trigonopsis variabilis (CBS 4095) and Rhodotorula glutinis (NCIMB 40412) have been covalently linked to Duolite A365, a polystyrenic support, functionalized with primary amino groups. The coupling to Duolite A365 was very effective for both enzymes, yielding an almost complete retention of the activity (>95%) in the case of the enzyme produced by T. variabilis. The immobilized D-amino acid oxidases exhibited a marked enhancement of stability against thermal and pH inactivation. The optimization of the reaction conditions, as well as the long-term operational stability, were studied in the case of the deamination of cephalosporin C.