Heat capacity of the high ionic conductor Ag8GeTe6 was measured between 10 and 320 K by using a high precision adiabatic calorimeter. Heat capacity anomalies were observed at 156.1, 169.9, 222.9 and 244.7 K, all of which were considered to be of the first-order phase transitions. The corresponding transition enthalpies are 90, 194, 2560 and 1910 J mol-1, and the transition entropies, 0.58, 1.14, 11.5 and 7.83 JK-1 mol-1, respectively. A large heat capacity jump of about 50 JK-1 mol-1 is observed at the transition of 244.7 K, above which the heat capacity decreases with increasing temperature. The negative temperature dependence of the heat capacity is analyzed on the basis of a Schottky-type mechanism.