The effect of heat treatment on the structure and morphology of α-MnO 2 nanorods with different potassium contents was investigated. These nanorods, prepared by ion exchange, were thermally treated at 500, 800, 1000 and 1100°C, and characterized with X-ray diffraction and electron microscopy. The structure and morphology of the starting sample remained preserved up to 500°C. The first structural and morphological changes were observed when α-MnO 2 nanorods with different potassium contents were heated at 800°C. The sample with the highest potassium content decomposed only partially to α-Mn 2 O 3 , while the decomposition of the α-MnO 2 to α-Mn 2 O 3 was complete in the sample with the lowest potassium content. Morphologically, both samples were composed of nanorods and grains. When the temperature was increased to 1000 and 1100°C, both the structure and morphology changed: the α-MnO 2 nanorods completely decomposed to Mn 3 O 4 grains. The acidic media in which the ion exchange took place shortened the α-MnO 2 nanorods.