Abstract In this study, the electrochemical behavior of diclofenac (DCF), a widely used NSAID drug, was undertaken at a modified glassy carbon electrode (GCE). A low-cost, sensitive, stable, and selective electrochemical sensor is proposed for the determination of this analyte by using differential pulse voltammetry in 0.10 M phosphate buffer solution, pH 8.00. At the Surface of GCE, EDOT (3,4-Ethylenedioxythiophene) was electropolymerized by chronocoulometry, the charge injected was carefully controlled. The polymerization parameters were 20.0 mM EDOT, H 2 SO 4 pH 1.50, step potential from 0.0 V to 1.1 V vs Ag/AgCl/KCl(sat), for 60 ms. The modified GCE displayed a significant enhancement of the anodic peak current compared to the bare electrode, measured by DPV. A calibration graph of the modified electrode exhibited an increase of the peak current about 63% with respect to the bare. The electropolymerized sensor was applied to DCF quantitation in pharmaceutical preparations with a relative standard deviation of 0.40%. It was also used in urine analysis. The limit of detection of this sensor was 9.06 nM compared to 1.37 μM for the bare electrode.