Tourism has become an important sector that has an impact on development of country economy. The main benefits of tourism are income creation and generation of jobs. For many regions and countries it is the most important source of welfare.The purpose of this study is to determine the most suitable months for human thermal comfort and tourism activities in west and North Westof Iran by using Physiologically Equivalent Temperature(PET).The data, which covering the period 1985–2010, from a dense network of 32 meteorological stations in west and north west f of Iran was used to compute the PET. Mean air temperature, relative humidity, vapor pressure, wind speed, and cloud cover data were obtained from theIran Meteorological Organization (IRIMO).Ray Man model was used to calculate the PET. Based on the calculations of PET in the region, it is shown that the monthsMarch and Decemberin the west parts of Kermanshah, the monthsApril, May and October in Kermanshah and Kurdistan and the June and September in the northern parts of the region such as Azerbaijan, and Hamadan are laying in the comfortable class that representing the most suitable months for tourism and tourist activities.