This study examines the association between annual levels of particulate matter (PM) and self-reported leisure-time physical inactivity (LTPI) in the Behavioral Risk Factor Surveillance System (BRFSS) among 63,290 survey respondents who participated in the 2001 BRFSS from 142 counties in the U.S. The average prevalence of self-reported LTPI was about 24.9% (SE = 0.3%), LTPI prevalence was positively associated with annual mean of PM.5 concentration (p < .0001). The authors demonstrate that LTPI was associated with PM2.5 pollution with statistical significance with and without adjustment for covariates (adjusted odds ration [OR] = 1.16; 95% CI: [confidence interval] 1.06-1.27). This study suggests that ambient PM2.5 air pollution is associated independently with LTPI. PM2.5 pollution and physical inactivity are both risk factors of chronic diseases. Therefore, it is important for environmental officials to implement measures to reduce ambient air pollution while public health officials simultaneously promote regular physical activity by encouraging the general public to remain physically active.