The oxidations of catechol to 1,2-benzoquinone by oxygen and hydrogen peroxide are catalyzed by tyrosinase and peroxidase, respectively. The tyrosinase reaction consumes oxygen but peroxidase reaction does not. Then, when hydrogen peroxide is added to the peroxidase containing solution in which tyrosinase reaction of catechol had taken place the consumption rate of oxygen in tyriosinase reaction should be decreased by the commencing peroxidase reaction because catechol works as a common substrate of both enzymatic reactions. In this work, the hydrogen peroxide sensor was fabricated by combining a bienzyme membrane with an oxygen electrode. This sensor response increased proportional to the added H2O2 (linear concentration range is from 5 x 10(-6) M to 2 x 10(-4) M with a detection limit of 2 x 10(-6) M). The use of the oxygen electrode with gas permeable membrane should increase the selectivity of the present H2O2 sensor because nonvolatile electroactive species in the sample solution are not detected.