The present study was focused on three aims: (1) preparation of the phase-change gypsum wallboard as novel phase-change wallboard incorporated with the eutectic mixture of capric acid (CA) and myristic acid (MA) for latent heat thermal energy storage (LHTES); (2) determination of thermal properties and thermal reliability of prepared phase-change wallboard using differential scanning calorimetry (DSC) technique; and (3) estimation of thermal performance of the phase-change wallboard in a simple building envelope. The maximum proportion of CA/MA eutectic mixture as phase-change material (PCM) absorbed in gypsum wallboard was about 25 wt% of total weight. No leakage of the PCM from the phase-change wallboard was observed after 1,000 thermal cycling. The melting and freezing temperatures and latent heats of phase-change wallboard were measured as 21.12 degrees C and 21.46 degrees C, 36.23 and 38.28 J/g, respectively, by DSC analysis. These properties make it functional as LHTES medium, which can be applied to peak load shifting, improving the use of waste heat and solar energy, as well as more efficient operation of heating and cooling equipment. In addition, the phase-change wallboard has good thermal reliability in terms of the changes in its thermal properties after 500 and 1,000 thermal cycling. Furthermore, thermal performance test indicated that the phase-change wallboard can be considered as an effective building element because of reducing the indoor temperature of the room approximately 4 degrees C and thereby improving thermal comfort of a building envelope.