The purpose of this study is to investigate the effect of Ondol on the bedclimate, microclimate and physiological responses of occupants. Four healthy female subjects slept for seven hours in thermal environment of detached house and apartment respectively. Their bedclimate, microclimate, skin temperature, weight loss of body, weight of bedcloth and sleepwear, body movement and subjective sensation were measureed for this study. The results were as follows; The differences of bedclimate, microclimate, skin temperature were significant according to season and residence styles. The occupants of the detached house showed higher temperature and humidity inside quilt and clothes than those of the apartment did on apartment environment. The occupants of the detached house showed higher weight losses of body, heavier weights of quilt than those of the apartment did on apartment environment in the spring, autumn and winter, lower weight losses of mattress in the autumn and winter. The occupants of the detached house moved more than those of the apartment on apartment environment when sleeping. The occupants of the detached house felt higher thermal sensation and lower humidity sensation than those of the apartment did. The occupants of the detached house felt more comfortable than those of the apartment on detached house environment, while the occupants of the apartment felt more comfortable than those of the detached house on apartment environment. The thermal environments of the apartment and the detached house had an effect on the bedclimates, microclimates of occupants and therefore the physiological responses such as skin temperature, rectal temperature, weight loss of body, perspiration and subjective sensation are different during sleeping according to their residential styles on the same environment.