In this study, 6-phosphogluconate dehydrogenase was covalently immobilized onto the N-2-aminoethyl-3-aminopropyltriethoxysilane (APTES) modified core-shell Fe3O4@SiO2 magnetic nanoparticles (ASMNPs) using glutaraldehyde (GA). Immobilization of 6PGDH on ASMNPs was confirmed using fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. The NADP(+) conversion ratio, the reusability, thermal, and storage stability of the immobilized 6PGDH were determined and compared with those of the free enzyme. The maximum retention of enzyme activity reached to 96% when the enzyme was immobilized on ASMNPs activated with monomer form of GA. Although the thermal stability of free and immobilized enzymes was similar, at 30 degrees C, the immobilized 6PGDH showed the improved thermal stability at 40 degrees C and 50 degrees C compared with free 6PGDH. While the free 6PGDH only converted 33% of NADP(+) in reaction medium upon 480 s, the immobilized 6PGDH performed 56% conversion of NADP(+) at same time. The immobilized 6PGDH retained 62% of its initial activity up to the fifth cycle and 35% of its initial activity after 22 days of storage at 4 degrees C.