A hetero-oligomeric glucose dehydrogenase (GDH) from a moderate thermophilic bacterium, SM4 was crosslinked with glutaraldehyde (GA) and it now showed only one optimum temperature for reaction at around 65 degrees C, which approximately follows the Arrhenius equation. The native enzyme had shown optima at both 45 degrees C and 75 degrees C. In addition to the alteration of the optimum temperature for reaction, GA cross-linked GDH retained more than 90% of its initial activity even after 30 min of incubation at 65 degrees C.