Phase change material (PCMs) is used to equilibrate the temperature fluctuation and to store energy in several practical application areas such as electronics, automobile industry and also buildings. In this paper, an example of the application of phase change material in the building application is investigated. The physical problem of phase change is solved by using a numerical study based on the finite element method. The PCM selected in this study, is incorporated directly within the building materials for improving its capacity of thermal storage. Two different building materials are selected according to their usual applying as construction materials for residential buildings. The numerical results have been checked and validated with an experimental model and the error is estimated. The results reveal the potential of PCM in the enhancement on the thermal inertia of the wall and effectively reduced the fluctuation of the interior surface temperature. In addition, with the increasing filling amount of PCM, the thermal response of the building material will be more effective through improving its thermal insulation and stored more of energy as a latent heat.