Immobilized enzyme membrane

An enzyme electrode apparatus for electrochemically analyzing a substance in a sample solution, which comprises a vessel for encasing an electrolyte solution therein;

• an anode;
• a cathode;
• an immobilized enzyme membrane containing a skin layer that functions as a barrier provided at a working face of the anode and/or cathode;
• and an electrolyte solution in the vessel;
• the immobilized enzyme membrane being provided by an asymmetrical membrane having a thickness of 30-300 .mu.m integrally formed from a skin layer substantially incapable of permeating an enzyme therethrough, but capable of permeating a gas and a liquid therethrough, and a sponge layer having sufficient porosity for retaining a necessary amount of the enzyme and pores intercommunicated with one another throughout the sponge layer, the enzyme being immobilized in the pores of the sponge layer by cross-linking, the skin layer having a thickness of 0.1-3 m m and the sponge layer having a porosity of 50-90%;
• the skin layer and the sponge layer being formed from the same material.