Passive cooling of buildings is one of the energy-saving measures that can be employed in climateswith predominantly sensible cooling loads. There are several passive cooling techniques that can be used in buildings; among them night-time ventilation. Night-time ventilation cooling utilizes diurnalswing of outdoor temperature and it has been used in many buildings. However, this passive coolingtechnique only works well when a building has a sufficient thermal mass. In case of heavy-weightbuilding structures (brick, stone, concrete etc.) building structures themselves form a thermal storagemass. On the other hand, a purpose-provided thermal storage capacity may need to be added to lightweight building structures in order to make night-time ventilation cooling work effectively.Phase change materials seem to be a very promising medium for thermal storage in manyapplications including passive cooling of buildings. The advantage of phase change materials (PCMs) in comparison with sensible heat storage materials is the ability of PCMs to store huge amount of heat in a narrow band of temperature around the melting point due to absorption and release of latent heat. A set of experiments both laboratory and full scale have been carried out in order to investigate the performance of latent heat storage in passive cooling of buildings.