The relationship between breast cancer mortality and air pollution was examined using an ecological design. The study areas consisted of 61 municipalities in Taiwan. Air quality data for recorded concentrations of fine particulate matter (PM2.5) from study municipalities for 2006–2009 were obtained as a marker of traffic emissions and were used as a proxy for polycyclic aromatic hydrocarbons (PAHs) exposure. Age-standardized mortality rates for breast cancer mortality were calculated for the study municipalities for the years 1999–2008. A weighted multiple regression model was used to calculate the adjusted risk ratio in relation to PM2.5 levels. Results showed that individuals who resided in municipalities with the highest PM2.5 were at an increased risk of death from breast cancer. This study is the first to suggest that exposure to high levels of PM2.5, a proxy measure of PAHs, may be associated with an increased risk of death from breast cancer. The findings of this study warrant further investigation into the role of air pollutants in the risk of breast cancer.