Partially purified alpha-Galactosidase from Penicillium griseoroseum was immobilized onto modified silica using glutaraldehyde linkages. The effective activity of immobilized enzyme was 33%. Free and immobilized alpha-galactosidase showed optimal activity at 45 degrees C and pH values of 5 and 4, respectively. Immobilized alpha-galactosidase was more stable at higher temperatures and pH values. Immobilized alpha-galactosidase from P. griseoroseum maintained 100% activity after 24 h of incubation at 40 degrees C, while free enzyme showed only 32% activity under the same incubation conditions. Defatted soybean flour was treated with free and immobilized a-galactosidase in batch reactors. After 8 h of incubation, stachyose was completely hydrolyzed in both treatments. After 8 h of incubation, 39% and 70% of raffinose was hydrolyzed with free and immobilized alpha-galactosidase respectively. Immobilized a-galactosidase was reutilized eight times without any decrease in its activity.