In this research, the thermal decompositions of β-manganese dioxide (β-MnO2) 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°C: the decomposition of β-MnO2 to Mn2O3 and of this oxide to Mn3O4 in both nitrogen and air. β-MnO2 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 β-MnO2 exhibits higher values of the activation energy (E a) 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.