ABSTRACT This study is one of the first to examine the causal impact of ozone pollution on stroke hospitalization in a developing country, using individual-level inpatient medical records from a major Chinese city. Employing an instrumental variable (IV) approach with thermal inversion to address potential endogeneity in air pollution, our findings reveal ozone pollution has statistically significant effect on total health expenses across all exposure intervals, spanning from 1 day to 14 days. The impact of exposure to ozone pollution for less than 7 days on total expenses can be primarily attributed to changes in daily expenses, while the impact of exposure for more than 7 days is associated with an increase in the length of hospital stay. This effect, largely driven by out-of-pocket spending on medication and examination costs, is more salient for females and ischemic stroke patients.