The Cu+ oxidation reaction study in the PbZr0.50Ti0.44(Cu1/4Nb3/4)(0.06)O-3 + 0.5 mol%MnO2 ferroelectric ceramic was carried out using high-resolution themogravimetry (Hi-Res TGA) and the kinetic analysis was made by using the traditional criterion of the mathematical fitting of f(alpha) functions and the isoconversion method. A D2 diffusion mechanism with a variable activation energy value in the range 75-103 kJ/mol was obtained and the results were interpreted in two ways: an intercrystallite oxygen diffusion and a copper(I) oxidation process.