BACKGROUND : Epidemiological evidence on the association between short-term exposure to fine particulate matter (PM2.5) air pollution and acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is limited in China. OBJECTIVE : To explore the associations between PM2.5 and AECOPD in Yancheng, China from 2015 to 2017. METHODS : In this time-series study, we used a generalized linear model with quasi-Poisson regression to investigate the association between PM2.5 and AECOPD admitted in two major hospitals in Yancheng. We tested the robustness of the associations using two-pollutant models and examined the potential effect modification by age, gender and season via stratification analyses. Lastly, we fitted the concentration-response curves. RESULTS : We identified a total of 4761 AECOPD inpatients during the study period. The average daily-mean PM2.5 concentration was 45.2 μg/m3. Each 10 μg/m3 increase in PM2.5 concentration on the concurrent day of the onset of AECOPD was associated with a 1.05% (95% confidence interval: 0.14%, 1.96%) increase in AECOPD. The association was robust to the adjustment of ozone, but not to sulfur dioxide, nitrogen dioxide, and carbon monoxide. The association was larger in females, elderly patients, and was restricted within the cold season, but all between-group differences were insignificant. The concentration-response relationship curves were generally linear but flatted at concentrations over 40 μg/m3. CONCLUSIONS : This study demonstrated a higher risk of AECOPD associated with present-day PM2.5 exposure in a Chinese city. We further provided important information on lag patterns, susceptible subgroups, sensitive seasons, as well as the characteristics of the concentration-response relationship curves.