A glassy carbon electrode modified with reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) was developed for the individual and simultaneous determination of nimesulide and piroxicam. The electrochemical behaviour of the electrode was investigated by cyclic voltammetry and square wave voltammetry (SWV), under optimized conditions. Using SWV, the rGO-PEDOT:PSS/GCE sensor provided analytical curves in the concentration ranges 8.7 x 10(-7) -2.6 x 10(-5) M and 8.0 x 10(-8) -1.9 x 10(-6) M for piroxicam and nimesulide, with detection limits of 1.0 x 10(-7) and 2.4 x 10(-9) M, respectively. The rGO-PEDOT:PSS/GCE sensor showed good stability, repeatability, and reproducibility, with a high peak current and low working potential (electrocatalytic activity) during the electrochemical measurements. The device was successfully used to analyze river water and pharmaceutical samples, with results similar to those obtained using a spectrophotometric comparative method.