We present an electroanalytical method using square-wave anodic stripping voltammetry on electrochemically-treated screen-printed gold electrodes to the simultaneous determination of lead(II), copper(II) and mercury(II) in struvite (natural fertilizer produced from urine). Electrochemical treatment via cyclic voltammetry of the working electrodes increased surface rugosity that improved the electroanalytical responses for the three metals. Under optimized conditions and using a deposition time of 90 s, the proposed method presented the following limit of detection values: 1.3 µg L-1 for lead(II), 2.0 µg L-1 for copper(II) and 0.9 µg L-1 for mercury(II). Struvite samples were easily dissolved in supporting electrolyte solution (0.05 mol L-1 HCl). Satisfactory recovery values between 91 and 111% were obtained for the analysis of spiked samples. Hence, we can infer that the proposed electroanalytical method is an effective alternative for the determination of trace metals, since it provides precise and accurate direct analyses, with rapid responses without interference from sample matrix and enabling in field analysis.