In this paper, the cyclic voltammetry technique was used to investigate the redox properties of a carbon paste electrode (CPE) modified by a synthesized Schiff base (PNH) and oxidized multiwall carbon nanotubes (OCNTs). The effect of oxidization of carbon nanotubes on the charge transfer rate constant of the PNH was studied. Also the electrocatalytic activity of the modified electrode for oxidation of isoprenaline (IP) via EC' mechanism was described. The oxidation of IP at modified electrode occurs at a potential about 315 mV less positive than at unmodified carbon paste electrode. The value of catalytic rate constant was calculated for IP, using chronoamperometry. Based on square wave voltammetry, the oxidation of IP exhibited a dynamic range between 1.0 and 1800.0 mu M and a detection limit (3 sigma) of 0.3 mu M. Also, simultaneous determination of IP and captopril (CA) was described at the modified electrode. Finally, this electrode was used for the determination of these substances in synthetic solutions and IP injections. (C) 2013 Elsevier B.V. All rights reserved.