Glassy carbon electrode modified with functionalized multi-walled carbon nanotubes within a dihexadecyl hydrogen phosphate film was used to develop a sensitive and simple square-wave adsorptive stripping voltammetric (SWAdSV) method for the determination of gemfibrozil. The cyclic voltammograms obtained showed one irreversible anodic peak for gemfibrozil at a potential of 1.3 V using a 0.1 mol L-1 phosphate buffer solution (pH 2.0). The cyclic voltammetric responses were studied with regard to scan rate, and the number of electrons transferred during the oxidation process was calculated. A calibration curve for gemfibrozil in the concentration range from 75 to 1000 nmol L-1 with a detection limit of 53 nmol L-1 were obtained. The proposed SWAdSV method was successfully applied to determine gemfibrozil in pharmaceutical and urine samples with good accuracy and precision. (C) 2012 Elsevier B.V. All rights reserved.