The chemical constituents of fine particulate matter (PM_2.5) vary by source and capacity to participate in redox reactions in the body, which produce cytotoxic reactive oxygen species (ROS). Knowledge of the sources and components of PM_2.5 may provide insight into the adverse health effects associated with the inhalation of PM_2.5 mass. We collected 48 h household and personal PM_2.5 exposure measurements in the summer months among 50 women/household pairs in a rural area of southwestern China where daily household biomass burning is common. PM_2.5 mass was analyzed for ions, trace metals, black carbon, and water-soluble organic matter, as well as ROS-generating capability (oxidative potential) by one cellular and one acellular assay. Crustal enrichment factors and a principal component analysis identified the major sources of PM_2.5 as dust, biomass burning, and secondary sulfate. Elements associated with the secondary sulfate source (As, Mo, Zn) had the strongest correlation with increased cellular oxidative potential (Spearman r: 0.74, 0.68, and 0.64). Chemical markers of biomass burning (water-soluble potassium and water-soluble organic matter) had negligible oxidative potential, suggesting that these assays may not be useful as health-relevant exposure metrics in populations that are exposed to high levels of smoke from household biomass burning.