In this study, ZnO nanoparticles and multiwalled carbon nanotubes (MWCNTs) modified carbon paste electrode (CPE) was used as a fast and sensitive tool for the investigation of electrochemical oxidation of naproxen in biological pH. The study was carried out by using cyclic voltammetry (CV), chronoamperometry, and square wave voltammetry (SWV) techniques. Some parameters such as the electron transfer coefficient (alpha) and diffusion coefficient (D) were also determined for the naproxen oxidation. Naproxen was detected over a linear concentration range of 1.0 x 10(-6) M to 2.0 x 10(-4) M by square wave voltammetry. The limit of detection was obtained as 2.3 x 10(-7) M. The modified electrode shows good selectivity toward naproxen in the presence of some inorganic cations and sugars. Finally, the electrochemical oxidation of naproxen at the surface of ZnO/MWCNTs/CPE employed for the voltammetric determination of naproxen in pharmaceutical formulations. (C) 2014 Elsevier B.V. All rights reserved.