For the purpose of avoiding interference with glucose biosensing caused by coexisting easily oxidizable compounds, the sensing was attempted with an enzyme electrode (PANI/PAA-GOx/Cat) that was fabricated by co-immobilizing glucose oxidase (GOx) and catalase (Cat) on polyaniline/poly(acrylic acid) (PANI/PAA) composite films. The glucose sensing was carried out by monitoring the decrease in the O-2 reduction current resulted from competitive consumption of dissolved O-2 caused by electrochemical O-2 reduction and enzymatic glucose oxidation. It was found that the immobilized Cat reproduced O-2 from H2O2 accompanying GOx-catalytic glucose oxidation. As a result, the enzyme electrode gave a wide linear range (up to 1.6 +/- 0.0 mM glucose) and a high sensitivity (49.3 +/- 0.6 mu A cm(-2) mM(-2)) in the glucose sensing due to increased O-2 concentration in the vicinity of the enzyme electrode. The linear range and sensitivity of the electrode are obviously higher than those of the enzyme electrode without Cat (PANI/PAA-GOx). In contrast, despite the complexity of the electrode reaction, the detection limit of the PANI/PAA-GOx/Cat (26.5 +/- 5.2 mu M) was almost same as that of the PANI/PAA-GOx. Moreover, high glucose selectivity was achieved by adopting a bioelectrochemical system which functions at a low potential to avoid the interference of coexisting easily oxidizable compounds.