This paper presents the single-electrode Peltier heat of cathodic (or anodic) reaction of Li-Al alloy electrode in a coexisting phase state, or an intermetallic compound phase state estimated by thermoelectric-power measurement. The thermoelectric-power measurements of Li-Al alloys in various coexisting phase states were carried out with both potentiometric and potential-sweep methods in the LiCl-KCl eutectic system between 673 and 843 K. The values of the thermoelectric power of Li-Al alloys calculated by using thermodynamic literature data were in good agreement with those obtained by experiment. The single-electrode Peltier heat changes drastically with change of its phase state, and it was found that the formation reactions of beta (Li0.5Al0.5) and gamma (Li0.6Al0.4) phases are exothermic, and those of liquid phase from beta and gamma phase are endothermic. The single-electrode Peltier heat for the cathodic formation reaction of Li-Al alloy in intermetallic compound gamma phase is estimated to be exothermic by using the measured values of thermoelectric powers of Li-Al alloys in (beta + gamma) and (gamma + liq.) regions.