Residents completed a questionnaire survey assessing indoor environment and residents' behavior (i.e. when they opened windows/doors, when they operated air conditioners, and so on) during the period of ventilation measurement. The purpose of this study is to measure the ventilation rate in occupied dwellings in Kagoshima City, located in the southern part of Japan, using the tracer gas method and to investigate the relationship between the occupants' behavior in each dwelling and the energy consumption for air conditioning during the summer period. Based on the continuous measurement of the ventilation rate in eight dwellings, the proportion between the total ventilation rate (ventilation rate during occupancy of the dwellings) and the basic ventilation rate (ventilation rate during non-occupancy and with door/windows closed) is discussed. The measuring principle applied is the constant concentration tracer gas method. The main conclusion is that there is a large difference between the mean basic ventilation rate and the mean total ventilation rate. Lf the size of the basic ventilation rate and the user influenced ventilation rate in the investigated dwellings are compared, it can be seen that 87% of the total air change rate is caused by the behavior of the occupants.