No evidence exists concerning the association between blood pressure and ambient particles with aerodynamic diameter <= 1.0 mu m (PM1), a major component of PM2.5 (<= 2.5 mu m) particles, and potentially causing more hazardous health effects than PM2.5. We aimed to examine the associations of blood pressure in adults with both PM1 and PM2.5 in China. In 2009, we randomly selected 24,845 participants aged 18-74 years from 33 communities in China. Using a standardized mercuric-column sphygmomanometer, we measured blood pressure. Long-term exposure (2006-08) to PM1 and PM2.5 were estimated using a spatial statistical model. Generalized linear mixed models were used to evaluate the associations between air pollutants and blood pressure and hypertension prevalence, controlling for multiple covariates. A 10-mu g/m(3) increase in PM1 was significantly associated with an increase of 0.57 (95% CI 0.31-0.83) mmHg in systolic blood pressure (SBP), 0.19 (95% CI 0.03-0.35) mmHg increase in diastolic blood pressure (DBP), and a 5% (OR = 1.05; 95% CI 1.01-1.10) increase in odds for hypertension. Similar associations were detected for PM2.5. Furthermore, PM1-2.5 showed no association with blood pressure or hypertension. In summary, both PM1 and PM2.5 exposures were associated with elevated blood pressure levels and hypertension prevalence in Chinese adults. In addition, most of the pro-hypertensive effects of PM2.5 may come from PM1. Further longitudinal designed studies are warranted to validate our findings.