This work reports the use of iron tetrapyridinoporphyrazine (FeTPyPz) as a highly selective catalyst in the construction of an electrochemical sensor for estradiol valerate (EV) determination. The sensor was prepared by modifying a carbon paste with FeTPyPz. The best results were obtained in a mixture of acetonitrile (MeCN) and 0.1 mol L-1 phosphate buffer solution (pH 6.0) in a volume ratio of 47 : 53. A linear response range was observed between 45 and 450 μmol L-1 with a sensitivity of 12160 ± 306 μA L mol-1 and quantification and detection limits of 45 and 13 μmol L-1, respectively. The repeatability, expressed as the relative standard deviation (RSD) for n = 10, was 5.9% ([EV] = 50 μmol L -1). The reproducibility (RSD) for the sensor construction was better than 4% and the operational stability (RSD) over 50 measurements was 1.8%. A detailed investigation regarding the selectivity and electrochemical characteristics was carried out. Finally, in a first step to evaluate the application potential of the sensor, it was successfully applied to determine EV in a commercial formulation. © The Royal Society of Chemistry 2008.