Several studies with animal research associate air pollution in Alzheimer’s disease (AD) neuropathology, but the actual impact of air pollution on the risk of AD is unknown. Here, this study investigates the association between long-term exposure to ozone (O₃) and particulate matter (PM) with an aerodynamic diameter equal to or less than 2.5 μm (PM_2.5), and newly diagnosed AD in Taiwan. We conducted a cohort study of 95,690 individuals’ age ≥ 65 during 2001–2010. We obtained PM₁₀ and O₃ data from Taiwan Environmental Protection Agency during 2000–2010. Since PM_2.5 data is only accessible entirely after 2006, we used the mean ratio between PM_2.5 and PM₁₀ during 2006–2010 (0.57) to estimate the PM_2.5 concentrations from 2000 to 2005. A Cox proportional hazards model was used to evaluate the associations between O₃ and PM_2.5 at baseline and changes of O₃ and PM_2.5 during the follow-up period and AD. The adjusted HR for AD was weakly associated with a raised concentration in O₃ at baseline per increase of 9.63 ppb (adjusted HR 1.06, 95% confidence interval (CI) 1.00–1.12). Further, we estimated a 211% risk of increase of AD per increase of 10.91 ppb in O₃ over the follow-up period (95% CI 2.92–3.33). We found a 138% risk of increase of AD per increase of 4.34 μg/m³ in PM_2.5 over the follow-up period (95% CI 2.21–2.56). These findings suggest long-term exposure to O₃ and PM_2.5 above the current US EPA standards are associated with increased the risk of AD.