Night purge ventilation is an effective technique for passive cooling, which is typically used in office buildings with the aim of reducing the daytime temperature, and thereby reducing the cooling load of HVAC systems. This method uses the cool of the night to release the warmth stored in the thermal mass during the day. That is, this system optimizes the energy storage properties of thermal masses to provide thermal comfort in interior spaces. The purpose of this study is to determine the impact of the use of night purge ventilation in conjunction with PCMs on the indoor thermal conditions of a typical office building located in hot-arid climates. In this article, the impacts of optimal night ventilation on the heat flushing operation, inside room temperature and element thermal conditions are all evaluated. It was found that combining PCMs with night ventilation will significantly improve indoor thermal conditions; however, results vary for different days in general and different structural elements in particular. Moreover, the application of PCMs can reduce night ventilation system problem of occupants feeling cold in the morning, whereas in the majority of work hours the temperature of inside element faces is approximately 0.5 degrees C lower than the room temperature, both of which improve thermal comfort. (C) 2017 Elsevier B.V. All rights reserved.