In China, heating, ventilation and air conditioning systems account for 40% to 60% of the energy consumed in office buildings. Despite the widely known benefits of using natural ventilation as a passive cooling method and the potential reduction in energy demand the implementation of this strategy may bring, most office buildings in China are not designed to be naturally ventilated and little work has been developed in this area. In particular, there is a significant gap in knowledge with regard to how occupants adjust their indoor environmental conditions to achieve thermal comfort by controlling the opening and closing of windows. Understanding the patterns of this behaviour, and the relationship between this and other indoor environmental factors, is of great significance to the study of thermal comfort and energy efficiency. In this study, the authors attempted to demonstrate the relationship between the occupant behaviour with regard to window control and various indoor environmental factors, mainly through empirical data collected during field studies in Zhejiang province (a typical area with the climate of hot summer and cold winter in China). Field measurements and the results of questionnaires were correlated to establish the patterns of window openings in a naturally ventilated office building. It was found that window state changes mainly happen at the moment of occupant arrival and leaving, and a clear relationship between occupant window control behaviour, indoor temperature and indoor air speed was identified.