In relation to the issues of global warming and “heat island phenomena”, it is important to assess individual exposures to during hot period for health risk assessment in regions concerned. Although the authors have been studying directly individual exposure to temperature with using portable instruments, its results will be reported separately. Apart from temperature measurements, individual self regulation of indoor temperatures with AC are also important, since most of the advanced regions, residence has now been equipped with AC in most cases for controlling exposed temperature level. So far air conditioner (AC) use has been investigated especially in relation to the mitigation in terms of energy consumption and reduction of green house (GH) gas emission. Thus, this study was planned to see self regulation of temperature exposure and heat-related symptoms by different climate regions so that a questionnaire study has been conducted. Among 16, 100 people who were selected and requested to answer to our questionnaire by mail, eligible responses were collected for 2090 (recovery rate=l3 %) When the subjects were categorized into “Hokkaido” (cold area), “Honshu/Kita-Kyushu” (intermediate area) and “Okinawa” (subtropical area). AC for cooling was used in 40% in Hokkaido but in 90% + in other areas. Among AC users, people who use AC “whenever they feel hot” were 238 (“whenever group”), while those who use cooler “only when they feel intolerable” (“intolerable group”) were 1156. Temperature when 60% of “whenever group” was switching on AC at 25-30°C, whereas 40 % of “intolerable group” was doing so at 30-35?C. This means all AC users are using AC at 35+°C, suggesting 35°C in terms of outdoor temperature is a “behavioral threshold” for AC use among Japanese. Among several heat stress-related complaints, most prevalent was “can't sleep well” (57 %) and then “fatigue or change in physical conditions” (28 %) with being highest in Okinawa. History of heat illnesses (heat stroke, “Necchu-Sho” ), however, was least prevalent in Okinawa among the regions. In contrast in Hokkaido they were more frequent with including more people who reported recurrent events. Thus, it is likely that Hokkaido would be the most vulnerable to heat-related health stress especially among people who have not been using AC use and also those with high individual susceptibility with heat illnesses, whereas complaints about heat-related sleep disturbances are less prevalent in Hokkaido compared to other warmer regions. Finally, it should be noted that the present results might be biased through low rate of responses or due to questionnaire study. For your better understanding, please refer the other data on individual temperature exposure in 3 cities in Japan published separately.