The CAT/PANi/ITO bioelectrode has been prepared as a catalase biosensor and shows response for monitoring not only of $H_2O_2$ but also azide. The sensor exhibited an excellent response to the $H_2O_2$ and azide. The linear range of $H_2O_2$ was 0.064~1 mM and for azide 0.125~4 mM, respectively. Catalase biosensor was based on the principle of the measurements as the decrease in the differentiation of oxygen level, which has been caused by the inhibition of catalase in the bioactive layer of the biosensor by azide. The repeatability experiments were done in triplicate. The logarithm response of the biosensor to $H_2O_2$ ($r^2$ = 0.99), as well as, for azide ($r^2$ = 0.90) were reported, respectively. The bioelectrode was characterized by CV and AFM. The proposed biosensor would be applied for the determination of $H_2O_2$ and azide in various biological samples.