Aims/hypothesis: Worldwide, the information regarding the associations between long-term exposure to ozone (O3) and sulfur dioxide (SO2) and the development of type 2 diabetes remains scarce, especially in Asia. This study aimed to investigate the long-term effects of exposure to ambient O3 and SO2 on the incidence of type 2 diabetes with consideration of other air pollutants in Taiwanese adults aged 30 to 50 years. Methods: A total of 6,426,802 non-diabetic participants aged between 30 and 50 years old were obtained from the National Health Insurance Research Database between 2005 and 2016. Incident type 2 diabetes was the main diagnosis at medical visits. Air quality data were provided by the Taiwan Environmental Protection Administration. The air pollutant concentrations for each participant were estimated using the ordinary kriging method to interpolate daily concentrations of O3, SO2, carbon monoxide (CO), nitrogen dioxide (NO2), suspended fine particles (with an aerodynamic diameter less than 2.5 μm; PM2.5), and suspended particles (with an aerodynamic diameter less than 10 μm; PM10) in residential districts across Taiwan. Six-year average concentrations of pollutants were calculated from January 1, 2005 to December 31, 2010, and data were categorized into quartiles. We performed Cox regression models to analyze the long-term effects of exposure to O3 and SO2 on the incidence of type 2 diabetes. Results: The hazard ratio (HR) for the incidence of diabetes per each interquartile range (IQR) increase in ozone exposure (3.30 ppb) was 1.058 (95% confidence interval (CI): 1.053, 1.064) and 1.011 (95% CI: 1.007, 1.015) for SO2 exposure (1.77 ppb) after adjusting for age, sex, socioeconomic status, urbanization level, temperature, humidity, and chronic comorbidities (Model 3). Furthermore, for every 3.30 ppb increase of O3, the HR for incident type 2 diabetes was 1.093 (95% CI: 1.087, 1.100) after controlling factors shown in Model 3 plus SO2 and PM2.5. On the other hand, for every 1.77 ppb increase of SO2, the HR for incident type 2 diabetes was 1.073 (95% CI: 1.068, 1.079) after controlling factors shown in Model 3 plus NO2 and PM2.5. Conclusions: Long-term exposure to ambient O3 and SO2 was associated with a higher risk of developing type 2 diabetes for Taiwanese population. Exposure to O3 and SO2 may play a role in the adult early-onset type 2 diabetes.