The storage of thermal energy is one of the economic ways to achieve a rationalization of energy consumption in buildings and to ensure comfort conditions. The effect of using phase change materials on the room structure located in Egypt was studied using the PCM Express modeling and simulation program. The theoretical calculations were based on the PCM boards were impeded inside the walls. The study showed the importance of using phase change materials in the building structure compared to the traditional room due to the thermal efficiency of these materials and the storage and release of heat energy, which contributes to reducing thermal loads and good internal comfort conditions. Where five different cities were studied in Egypt (Cairo, Alexandria, Asyut, Aswan and Suez) and the study concluded that the city of Alexandria achieved the highest rise in energy saving by 2.59 kW/m3 day. The current study also demonstrated the effect of use of phase change materials with different thicknesses (5 mm, 10 mm and 15 mm). It is found that the thickness of 15 mm achieved higher energy saving by 2.34 kW/m3 day. Walls orientation (East, North, South, and West) were also studied, and it is found that the south wall higher energy saving by 1.92 kW/m3 day. Different PCM types was studied (Paraffin PCM, fatty acid PCM and hydrated salts PCM) and it is concluded that the higher energy saving was achieved by the values of 2.1 kW/m3 day, 1.7 kW/m3 day, 0.6 kW/m3 day for Paraffin PCM, fatty acid PCM, and hydrated salt PCM respectively. The conditions of internal comfort for the study rooms obtained the highest average increase in annual comfort temperature and energy saving by 38.9%