<p>Refinery workers are potentially exposed to methyl tert-butyl ether emissions. The present study aimed to investigate seasonal changes in health risks due to exposure to methyl tert-butyl ether among the workers of a refinery. Methyl tert-butyl ether samples were collected in summer and winter seasons. Samples were analyzed by gas chromatography equipped with flame ionization detection (GC-FID). The quantitative risk assessment approach designed by the United States Environmental Protection Agency (USEPA) is applied to evaluate risks associated with exposure to methyl tert-butyl ether. The findings revealed that the mean concentrations and non-carcinogenic risk of exposure to methyl tert-butyl ether were lower than acceptable limits among all workers and in various jobs in both seasons. Furthermore, the results indicated that the mean values of carcinogenic risk related to exposure to methyl tert-butyl ether in total workers were higher than acceptable value in both seasons. These values were greater than acceptable value in jobs of loading operator, repairman, and site man in summer and in job of loading operator and repairman in winter season. For all workers, the exposure and health risk values were greater during the summer compared to those in the winter. This study highlights a clear occupational health concern regarding chronic exposure to methyl tert-butyl ether, especially in high-risk jobs such as loading operators and repairmen during the summer season.</p>