Arthrobacter nicotianae cells, producers of glucose isomerase, were immobilized inside xerogel of silicium dioxide, and properties of the resulted heterogeneous biocatalysts were investigated in the process of isomerization of monosaccharide (glucose and fructose). The glucose isomerase activity of the resulted biocatalysts was shown to be 10 U/g, on average, taking into account the loss of the activity upon the immobilization, which amounted to 50% of the cell activity in suspension. The rate of the fructose isomerization increased linearly in the range of 55–80°C with the temperature coefficient 1.3. The biocatalysts were stable in this range; they were rapidly inactivated, however, at increasing temperature. The half-pife time of inactivation was six to seven h and five min or less at 80 and 85°C, respectively. The half-pife time of inactivation of heterogeneous biocatalysts was 50–90 h in the periodic process of isomerization of 2 M monosaccharides at 60°C in the presence of the immobilized Arthrobacter nicotianae cells.