Abstract: The reduction process of murexide (or ammoniumm purpurate) has been inves- tigated at gold minigrid electrode in optically transparent thin-layer cell, using UV-VIS spectroscopy technique. From the experimental results of thin-layer cyclic voltammograms of murexide (or purpurate ion) in different pH system and UV-VIS spectra from the reduction of purpurate ion obtained in situ by spectro- electrochemistry, it was found that the reduction of purpurate ion is a two electron transfer irreversible process, accompanied with a subsequent chemical reaction at pH<8 in which the reduction product, dibarbituylamine decomposed into uramil and barbituric acid. In addition, the formal potential, E~0′ and electron transfer number, n were calculated from spectra at different potentials. Double potentialstep chronoabsorptometry was employed for measuring the decomposition rate constant of dibarbituylamine. The pseudo-firstorder rate constants at pH4.0, 5.0, 5.5 and 6.4 were 6.6, 5.0, 3.4 and 2.6×10~(-4) s~(-1), respectively.