The indoor temperature and humidity of four cities which are located in different climatic zones in China were monitored continuously in summer. The results show that the indoor air temperatures varied in narrow bands in the cities and the indoor thermal conditions were far from the ASHRAE 55-92 summer comfort zone during most of the measuring period. The indoor thermal environment of naturally ventilated rooms of residential buildings in the four cities was evaluated by using the predicted mean vote (PMV) model and the adaptive comfort model (ACM). The difference of thermal satisfaction between the two results was analyzed and discussed, and the potential of energy conservation was estimated by applying the ACM. The results show that even if energy consumption of dehumidification under humid climatic conditions is taken into consideration, when ACM is employed to optimize the operative temperature of the ventilation systems with the occupants maintaining control of the indoor thermal environment, the potential of energy conservation can be roughly more than 20% over the whole summer season in the four cities. (C) 2012 Elsevier B.V. All rights reserved.