The thermal stability of flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus terreus in phosphate buffer solution was substantially improved by kosmotropic ions, especially kosmotropic anions. The residual activity of FAD-GDH in a 1.5 M sodium or ammonium sulfate solution remained more than 90 % after 60 min of heat treatment at 60°C, while slight activity was observed for FAD-GDH in a solution in the absence of additive sulfate ions. The stabilizing effect of the electrolytes was concentration-dependent and strongly related to the structural stabilization of the enzyme, which involved enzyme compaction.