Background <p>Socioeconomic inequality in air pollution exposure poses a significant public health challenge, yet little is known about how such disparities vary across levels of urbanization. This study aims to examine the association between socioeconomic status (SES) and PM_2.5 exposure in Taiwan from an urban-rural perspective.</p> Methods <p>This ecological study used township-level data from 2011 to 2020. PM_2.5 exposure estimates were generated using land-use regression and Ordinary Kriging models. Socioeconomic position was assessed using multiple SES indicators, including educational attainment. Inequality was quantified using the Slope Index of Inequality (SII) and the Relative Index of Inequality (RII).</p> Results <p>PM_2.5 concentrations were highest in metropolitan core areas and lowest in remote townships. Townships with higher SES experienced greater PM_2.5 exposure. SII and RII for the proportion of individuals with higher education showed a consistent increase over the study period, indicating worsening socioeconomic inequality. However, inequality patterns differed between urban and rural areas.</p> Conclusions <p>Substantial urban-rural disparities in PM_2.5 exposure and socioeconomic inequality were observed. The worsening trends highlight the need for immediate policy interventions to protect vulnerable populations and further research to identify and address pollution sources.</p> Graphical Abstract <p></p>