A simple surface modification method using sol-gel method was developed to immobilize an enzyme on the inner surface of a microreactor. In this study, a fused silica capillary used as a microreactor, and lipase was immobilized on it as a hydrolytic enzyme. After the sol-gel modification, a nanoporous structure was obtained on the inner surface of the microchannel. Compared with a batchwise reaction under similar conditions, the efficiency of enzymatic hydrolysis was greatly improved, and the reaction was complete within 30 sec. A decreased reaction yield with a microchannel of larger internal diameter revealed the strong influence of the diameter on the reaction efficiency.