Latent heat storage is an economical way to achieve energy efficiency and improve thermal comfort in buildings. In this research, the effects of using PCM Wallboards in a residential apartment envelop located in Homs was studied by PCM Express software. PCM wallboard with 23°C melting temperature was used and installed on the inner face of the walls and ceiling of the apartment. This investigation shows that the importance of using PCMs in buildings envelope, compared with conventional thermal insulation materials, due to the effectiveness of PCMs materials and storing and releasing of thermal energy, which contributed to reducing of thermal loads and improved the internal thermal comfort.