Coal fly ash (FA), an aluminum silicate by-product and environmental pollutant which is generated during the combustion of coal in coal-fired power stations, was used as an electrode modifier for the determination of Cd(II) in aqueous solutions. In this work, graphite/polyurethane-based composites containing different amounts of FA were prepared and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) thermogravimetry (TGA), and derivative thermogravimetry (DTG). The graphite/polyurethane composite electrodes (GPUE), with and without FA modifier, were evaluated with regard to their performance as voltammetric electrodes in the determination of metallic cations, using Cd(II) as a probe. After optimizing solution and instrumental parameters affecting the peak current, a differential pulse anode stripping voltammetry (DPASV) procedure was developed for GPUE modified with 5% FA (m/m), resulting in a linear response for Cd(II) from 2.0 x 10 −7 to 1.0 x 10 −6  mol L −1 with a detection limit (LOD) of 6.6 x 10 −8  mol L −1 . Cd(II) was added to natural water samples and determined at the 10 −7  mol L −1 level with a mean recovery of 99%. It was also extracted from exhausted rechargeable Ni-Cd batteries and diluted to ca. 0.2 µmol L −1 and determined with the same electrode, with recoveries of 98.7% when compared to FAAS. These results serve as a proof of concept that FA is a useful electrode modifier.