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Background Increasing evidence has shown ambient fine particles (PM_2.5) as a key risk factor to cardiovascular and metabolic diseases. However, few human studies examined if the adverse effects were associated carbonaceous particles, the potential toxic species in PM_2.5. Methods Based on AIRLESS project, we examined the changes in lipid profiles and blood pressure (BP) in response to acute exposure to ambient PM_2.5 and its carbonaceous compositions, namely elemental carbon (EC) and organic carbon (OC). 251 nonsmoking participants from urban (N=123) and peri-urban (N=128) Beijing, China, have completed 2 times clinical visits in winter, and another 2 in summer. During each visit, serum samples were collected for the lipid profile analysis of total cholesterol (TC), High-density lipoprotein cholesterol (HDL), Low-density lipoprotein cholesterol (LDL) and Triglycerides (TG), and BP were measured. Daily ambient PM_2.5, EC and OC were measured in the monitoring station nearby the participants’ communities. Associations between exposure and health outcomes were examined with linear mixed-effects model adjusted for demographic, socioeconomic and lifestyle parameters. Results Exposure to EC was significantly associated with all the cholesterol parameters, while PM_2.5 and OC were only associated with HDL. For example, an IQR increase in previous 1-day exposure to EC (3.9 μg/m³) was significantly associated with an elevation of HDL [1.4%(95% confidence interval (CI): 0.7-2.1%)], LDL [1.5%(CI: 0.3-2.7%)] and TC [1.3%(CI: 0.4-2.2%)] (p<0.05). All the three pollutants were significantly associated with the increase in systolic and diastolic BP, but not the changes in TG. A clear modified effect between sites were observed that may be partly attributed to the difference in the local emission sources given the significantly differed ratio of OC to EC between the two sites. Conclusions Elemental carbon may play an important role in the adverse cardiovascular and metabolic effect of PM_2.5.