The present study was aimed to assess the monthly changes in heat stress indices in outdoor environment during a 15-year period in Bandar-e-Abbas, Iran, as a representative of a dry and warm climate, based on meteorological data. The hourly meteorological data of air temperature and relative humidity from 2000 to 2014 (15 years) were obtained from the Iran Meteorological Organization. Three indices were considered to evaluate the degree of heat stress in outdoor environments: Wet-Bulb Globe Temperature Index (WBGT), Heat Index (HI), and Effective Temperature Index (ET). The highest average of WBGT index was in July (37.22 +/- 0.43 degrees C) during the studied years, and the lowest was in January (18.73 +/- 0.37 degrees C). The highest mean of heat index (HI) was in July (45.97 +/- 1.85 degrees C), and the lowest average of this index was in January (24.13 +/- 1.46 degrees C). In July, the effective temperature index (ET) had the highest average (31.02 +/- 0.22 degrees C) in July and the lowest (16.35 +/- 0.59 degrees C) was in January. On average, the WBGT index was higher than 28 degrees C (Very high status) in 55% of the days of the year, which indicates a high risk for outdoor workers in the case of heat stress. Moreover, 27% of the days experience very hot situation in terms of Heat Index. Regarding the results of the ET index, 41.2% of the days totally indicate very warm and sultry condition. There was a significant correlation between temperature and relative humidity with three studied indices (P<.001). According to the results, it should be noted that outdoor workers of Bandar-e-Abbas, have high and very high heat stress in the spring and summer (especially in July), which could lead to heat-related diseases. In this study, two important environmental parameters including air temperature and relative humidity were used for calculating the heat stress indices which were hourly measured at the weather stations.