PURPOSE: To perform accurate measurement over a long period of time by providing a conductive substrate and the conductive film containing the org. charge transfer complex crystal provided on the surface of said substrate and immobilizing enzyme in the conductive film and/or on the surface thereof.

CONSTITUTION: The electrode used in an enzyme electrode is constituted of a conductive substrate and the conductive film containing the org. charge transfer complex crystal provided on the surface of said substrate. As the conductive substrate, a metal such as copper, silver, platinum or gold, a carbon electrode, a substrate having a conductive layer composed of those conductive materials provided to the surface thereof by a vapor deposition means or a substrate formed from paste containing a powder of those conductive material can be used. The conductive film containing the org. charge transfer complex crystal is formed by adding the org. charge transfer complex crystal to an insulating polymer film so as to make said film conductive. For example, the film wherein the org. charge transfer complex crystal is grown in the thickness direction of the insulating polymer film so as to pierce the film shows conductivity.