Mesoporous silica powder (SBA15) with hexagonal pore structure (pore diameter, 7.5 nm and specific surface area, 584 m(2)/g) was prepared in the presence of tri-block copolymer as a template. Commercial mesoporous silica MCM41 with hexagonal pore structure (pore diameter, 2.9 nm and specific surface area, 759 m(2)/g) and SBA15 were used as a carrier for immobilization of a hydrolytic enzyme, lipase. SBA15 immobilized a greater amount of enzyme than MCM41 because of its larger pore diameter. The hydrolysis of 2-naphthyl acetate with the lipase immobilized in mesoporous silica was examined at 25, 50 and 70° C by measuring the concentration of hydrolysis product, 2-naphthol. At 50 and 75° C, the immobilized lipase converted a greater proportion of 2-naphthyl acetate than the lipase in aqueous phase, and the conversion with MCM41 as carrier was greater than that with SBA15. On reuse of the immobilized lipase a conversion of more than 70% was obtained at 50° C. The thermal stability of lipase for the hydrolysis of 2-naphthyl acetate was increased by the immobilization of lipase in mesoporous silica.