Abstract An UV spectroscopic method is proposed to analyze mixtures of the nitrofuran derivatives, nitrofurantoin, furaltadone and furazolidone, used in veterinary. The change of absorption spectra due to photo-decomposition is used. A 20% dimethylformamide/water, basic medium of pH 9.4 (ammonium chloride/ammonia) and a time of irradiation of 15 s are selected. Calibration graphs are established, with the percentage of decrease of absorbance as analytical signal, in the range 2–10 μg ml −1. To analyze mixtures of the three compounds the partial least-squares (PLS) multivariate analysis method is used with the spectra obtained by subtracting the spectra after irradiation to the original spectra. Good results have been obtained in the analysis of synthetic samples and a formulation containing all these compounds.