Catalytic effects of metal oxides with comparable surface areas on the decomposition of potassium perchlorate were studied by thermogravimetric analysis. The catalytic mechanism is discussed based on the relative activity of the metal oxides. It is found that the oxides containing transition metal cations with partially filled d-orbitals have the highest activities, the oxides containing transition metal cations with completely empty valence d-orbitals are moderately active, and the oxides containing metal cations with completely filled d-orbitals or noble gas configurations have the lowest activities. Differences between the decomposition of potassium perchlorate and the previously reported decomposition of sodium chlorate are explained by differences in the melting points and molecular structures of these salts.