The thermal decomposition of copper(II) permanganate has been studied between 335 and 370 K. Isothermal yield-time curves for the evolution of product oxygen (1.27 mol O2 per mol Cu(MnO4)2) were sigmoid shaped and data fitted the Avrami-Erofe’ev equation (n = 2) : [-ln(1 - alpha)]1/2 = kt, between 0.03 < alpha < 0.93 (where alpha is the fractional reaction). The activation energy for decomposition was 115 +/- 15 kJ mol-1. In the mechanistic discussion presented it is concluded that anion breakdown occurred at the interface between the crystalline reactant and an ill-crystallized, probably several constituent, disorganized mixture of residual products. Permanganate anion breakdown is believed to follow electron transfer to a Cu2+ ion (--> Cu+) that is subsequently reoxidized. A principal motivation for the work was as a route for the preparation of a non-stoichiometric, imperfect, microcrystalline mixture of transition metal oxides. The product of the present reaction is being investigated to determine its value as a precursor for the preparation of active heterogeneous oxidation catalysts.