A simple method integrating an immobilized enzyme reactor into a microchip electrophoresis device was developed. The enzyme immobilization into a microchip was performed by spotting and drying a drop of dissolved nitrocellulose (NC) on a glass substrate, and adsorbing enzyme on the reconstituted NC membrane. This enzyme-immobilized glass plate was assembled with a polydimethylsiloxane substrate on which the separation channel was fabricated. The advantage of this method is the ability to easily change the position and size of the reactor within the microchip electrophoresis device. A beta-galactosidase reaction was demonstrated with fluorescein di-beta-D-galactopyranoside using this integrated on-column enzyme reactor. A successful electrophoretic separation of its hydrolysis products, i.e., fluorescein mono-beta-D-galactopyranoside (FMG) and fluorescein, was achieved. Enzyme kinetics and inhibition of the beta-galactosidase using FMG and 2-phenylethyl beta-D-thiogalactoside, respectively, were also studied with microchip electrophoresis.