Food ingredients containing a-1,6-galactoside bonds elicit gastrointestinal disturbances in monogastric animals, including humans. Pretreatment of such ingredients with a-galactosidase (E.C 3.2.1.22) has the potential to alleviate this condition. For this purpose, a thermostable extracellular a-galactosidase from Debaryomyces hansenii UFV-1 was immobilized by method of covalent linkage in silica gel modified by amine groups, using the 3-aminopropyltriethoxysilane reagent. The immobilized a-galactosidase exhibited an activity of 40 U per g of silica and an activity yield of 50%. The optimum pH of free and immobilized a-galactosidase was 5.0. The optimum temperature of the free enzyme was 60 ºC and that of the immobilized enzyme was increased to 80 ºC. The enzyme immobilized showed more stability when compared to free a-galactosidase. Soymilk samples (5 mL) were incubated with 10.5 U of free a-galactosidase for 0, 2, 4 and 6 hours under shaking (100 rpm) at 60 ºC. For treatment with immobilized a-galactosidase, 1.0 g of silica containing 40 U of immobilized enzyme was incubated with 25 mL of soymilk in the same conditions for 0, 2, 4, 6, 8 and 10 hours. After treatment, the sugars found in the treated and non treated samples were extracted and analyzed by HPLC. The stachyose of soymilk was completely hydrolyzed by enzymes, after incubation for 4 hours, whereas that were detected reduction of 100% and 25% in the amount of raffinose by free and immobilized enzymes, respectively. After 10 hours of incubation 63% of raffinose was hydrolyzed by immobilized a-galactosidase. The immobilization of a-galactosidase enhanced of its thermal stability and wide pH range, increasing its capacity of utilization in soy products, but free a-galactosidase was more efficient, hydrolyzing completely raffinose and stachyose in soymilk.