Cognition of the bioclimatic conditions in any place can be the first step in conducting many environmental studies. This study was performed with the aim of determining the thermal stress of Iran. For this purpose, the daily data of the climatic variables in 288 synoptic stations were prepared from the Iran Meteorological Organization during the period 1981-2010. First, the bioclimatic conditions in each of the stations were calculated based on UTCI (Universal Thermal Climate Index) and PET (Physiologically Equivalent Temperature) indices. Then, using the thermal stress of 288 synoptic stations, the bioclimatic conditions throughout Iran were interpolated using a Simple Kriging method. The results of this study showed that the bioclimatic conditions are immensely varied spatially and temporally, such that in specific times all bioclimatic conditions can be seen in Iran. Also, during the year, each place can experience different bioclimatic conditions. Based on UTCI, extreme cold and extreme heat stress are the only bioclimatic conditions that do not exist during the year. However, based on PET, all bioclimatic conditions exist during the year. Also July and January, respectively, are the hottest and coldest months of the year. Based on UTCI in April, October and November, more than 70 % of Iran has comfortable conditions, whereas PET showed that in March and October 24.6 and 23.7 % experienced comfortable conditions respectively. It seems that the obtained results of PET index have high efficiency in relationship with UTCI index to show Iran’s bioclimatic conditions.
