In this research, the thermal decompositions of beta-manganese dioxide (beta-MnO(2)) under different atmospheres of dynamic nitrogen and air were investigated by TG, DTG, DSC and XRD techniques. Non-isothermal studies clearly indicate that two decomposition stages occur over the temperature regions of 30-1100 degrees C: the decomposition of beta-MnO(2) to Mn(2)O(3) and of this oxide to Mn(3)O(4) in both nitrogen and air. beta-MnO(2) decomposes at higher temperatures in air. The model-free kinetic analysis method together with the minimum deviation approach was employed to determine the activation energy (E(a)) and the kinetic model function (mechanism) of the thermal decomposition process from a series of thermogravimetric experiments. The results show that beta-MnO(2) exhibits higher values of the activation energy (E(d)) and the pre-exponential factor (A) in air. Compared with various solid state reaction models, the reactions are best described by the random nucleation and nuclei growth models. (C) 2011 Elsevier B.V. All rights reserved.