A simple and convenient method is described for voltammetric determination of thiamazole, a commonly used anti-hyperthyroid drug, based on its electrochemical oxidation at a multi-wall carbon nanotube modified glassy carbon electrode. Under optimized conditions, the proposed method exhibited acceptable analytical performances in terms of linearity (over the concentration range from 1.0 x 10(-7) to 5.0 x 10(-4) mol L-1, r = 0.9983), detection limit (3.0 x 10(-8) mol L-1) and reproducibility (RSD = 2.64%, n = 10, for 5.0 x 10(-5) mol L-1 thiamazole). To further validate its possible application, the method was used for the quantification of thiamazole in pharmaceutical formulations and biological fluids.