Abstract: An electrochemical sensor with sample pretreatment function includes an insulating substrate, and an electrode system disposed on the substrate having at least a working electrode and a reference electrode. An electrically insulating layer partially covers the electrode system, so an exposed area of the electrode system not covered by the electrically insulting layer forms an electrochemical electrode reaction region that accommodates sample solution and an air vent. A reaction layer is disposed in the electrochemical electrode reaction region and includes at least an oxidoreductase, an electron mediator, and at least a carrier.