beta-galactosidase splits lactose into glucose and galactose. Because of its biotechnological interest, we presented a biosensor system in order to monitor beta-galactosidase activity. Immobilization steps of the biosensor were identified by cyclic voltammograms and electrochemical impedance spectroscopy. beta-galactosidase was voltammetrically detected at about +150 mV (vs. Ag/AgCl) in citrate buffer solution (0.05 M, pH 4.8). The linear response for beta-galactosidase detection was in the range of 0.0118 U mL(-1) to 0.47 U mL(-1) and a shorter response time of similar to 50 s. Our results demonstrated the biosensor's electrochemical properties and analytical characteristics were very useful and effective for monitoring of beta-galactosidase activity.