Calorimetry of lithium-ion cells that were commercially available was carried out to characterize the thermal behavior of the cells during charge and discharge. The generated heat was mainly caused by the entropy change of the cell reaction and the electrochemical polarization. However, in the cell using non-graphitizable carbon material as the anode, complicated heat generation behavior was observed with hysteresis in charging and discharging voltage. Thermal behaviors due to crystal phase transition of the cathode active materials and due to variation of stage structure of graphitic carbon as the anode materials were also observed. Temperature dependency of the crystal phase transition of the cathode active materials was also discussed. Calorimetry could be one of effective methods to characterize the performance of lithium-ion cells.