BACKGROUND: The present study was conducted to investigate the probable changes in blood pressure of workers in coal mines. METHODS: In this study 91 workers, who worked in forwarding, preparation and exploitation units of coal mines and were in direct contact with carbon dioxide gas (from fireworks), have been selected as the case group, and 70 workers, who did not have direct contact with this gas, from other units were selected as the control group by simple random sampling method. The inclusion criteria were over 10 years of work experience and the age range of 30 to 45 years. The blood pressure values and their classification were determined based on the Seventh Report of the Joint National Committee on Prevention of Hypertension. Statistical analysis was performed using t-test. RESULTS: The results of this study showed that mean systolic and diastolic blood pressures in the case group were significantly lower than the control group (P < 0.001). CONCLUSION: The mean diastolic blood pressure of workers in coal mines is less than other people due to the CO2 gas. A greater control of the existing gas in mines by relevant factors is required. Necessary medical care and support measures should also be considered. Keywords: Blood Pressure Changes, Workers, Coal Mine.