A simple electroanalytical method was developed to determine the antibiotic ceftiofur (CF) in milk. The method is based on the adsorptive accumulation of the drug on a hanging mercury-drop electrode (HMDE) and the accompanying initiation of a negative square wave, which yielded well-defined cathodic peaks at -0.60 V (1C) and -0.91 V (2C) vs. Ag/AgCl. Calibration graphs were constructed and statistical parameters were evaluated. At pH 2.5, the square-wave voltammetry method revealed linearity from 52.4 to 524 ng mL(-1) (r = 0.997), which is in accordance with the tolerance level of 100 ng mL(-1) for CF as a residue in bovine milk established by the Food and Drug Administration (FDA) and the European Union. The limits of detection and quantification were 1.86 and 6.20 ng mL(-1), respectively. The method was tested to determine CF in spiked milk samples using HPLC as reference method.