The low energy excitation (LEE) mode measured in superionic conductors and the study by the low temperature heat capacity are discussed. The neutron inelastic scattering observed the LEE mode in Ag, Na and Cu ion conductors. The observation of the heat capacity offers an important information to specify the LEE in the superionic conductors. This mode might be one of the characteristic featuresof superionic conductors. Namely materials which show the superionic property in the high temperature phase exhibit the characteristic feature of the LEE mode in its low temperature phase. The characteristic features of the LEE mode are investigated theoretically.