Thiol monolayers prepared on gold electrodes have been proved to be useful as the anchor layers to immobilize enzymes molecules. An ion complex layer containing enzyme molecules can be prepared by the co-adsorption of the enzyme and poly-L-lysine onto a mercaptopropionic acid-modified gold surface. Enzymes, such as glutamate oxidase, glucose oxidase and lactate oxidase, were immobilized with high surface densities, and the enzyme-immobilized electrodes could be used for detecting the corresponding enzyme substrate. The UV irradiation onto the surface of gold electrode modified with an N-3-functionalized thiol in an enzyme solution produced an enzyme layer. which was formed through the photoreaction between the N-3-group and enzyme molecule. The activity of the immobilized enzyme (glucose oxidase) was rather low. However, the photochemical method is still interesting because it can provide the photolithographic patterning of enzyme layers.