Amyloglucosidase from Novo (Copenhagen, Denmark) was immobilized in controlled pore silica particles with the silane-glutaraldehyde covalent method. Thermal stability of the free and immobilized enzyme (IE) was determined with 30% (wiv) alpha-amylase liquefied cassava starch, pH 4.5, temperatures from 35 to 75 degrees C. Free amyloglucosidase maintained its activity practically constant for 240 min and temperatures up to 50 degrees C. The IE has shown higher stability retaining its activity for the same period up to 60 degrees C. Half-life for free enzyme was 20.6, 6.44, 2.07, 0.69, and 0.24 h for 55, 60, 65, 70, and 75 degrees C, respectively, whereas the IE at the same temperatures had half-lives of 116.4, 30.88, 8.52, 2.44, and 0.73 h. The energy of thermal deactivation was thus 50.6 and 57.6 kcal/mol, respectively for the free and IE, confirming stabilization by immobilization.