Background and aims: A glance at different occupations and production processes showed that one of the important and popular occupational health problems in the workplace is improper climate conditions such as hot environments .In this condition the core body temperature may increase and cause some diseases, occupational accidents and reduction of efficiency. The purpose of this study is determination of heat stress and its risk assessment in a steel factory. Methods: In order to survey heat stress, a cross-sectional study was conducted in a steel factory in Ahwaz in the autumn season and WBGT index was used as a standard method for heat stress measurement. After measurement of WBGT index, the results were compared to ACGIH_TLV. In the second stage, for the assessment of probable heat hazard, psychometric conditions of work place along with some other parameters like work load, kind of occupation, distance between workplace and rest areas, water consumption and uses of personal protective devices were taken into account In this area, it was tried to determine the existence of improper probable heat condition with regard to priority and necessity for modifications. Results: After measurement in production process, other workshops and administrative office, the data were compared to ACGIH standards .The results showed that the workplace had acceptable climate conditions from heat stress with 81.1 %and there were no acceptable climate conditions with 18.9 %which is above TLV. The workplaces heat risk assessment showed that their conditions with 14.3%, 49.3 % and 36.4% were in level one to three respectively. Conclusion: Although the fall season in regions such as Khuzestan is cooler than summer, but employment in industries such as steel due to its exothermic process, a threat to the health of these kinds of workers. The heat conservation planning should not only be limited to the summer season. More research in the spring and even winter are recommended. [ABSTRACT FROM AUTHOR]