Xuanwei and Fuyuan, located in the Yunnan province in southwest of China, are known to have a high incidence of lung cancer caused by indoor airborne polycyclic aromatic hydrocarbons (PAHs) generated during bituminous coal combustion for heating and cooking in unvented households. In this study, indoor and outdoor air was sampled at 38 sampling sites around these areas in January 2007. The concentrations of 16 PAHs were analyzed. The sources of PAHs in these two counties were also investigated. Quartz filters and polyurethane foam were used to collect particle-bound PAHs (p-PAHs) and gas-phase PAHs (g-PAHs), respectively. The concentrations of benzo(a)pyrene (Bap), the best index for PAHs carcinogenicity, were higher in indoor air than that in outdoor air. Bap levels in all the indoor air samples were higher than the national criteria (1.0 ng m⁻³) in China, but were much lower than those in previous studies in the same areas. Bap levels in 20 out of the 29 outdoor air samples were higher than the national criteria (10 ng m⁻³) of China. Significant differences in the gas/particle partition of PAHs were found between the indoor and the outdoor air samples. Principal component analysis (PCA) in combination with diagnostic ratios indicated that coal combustion was the predominant source for both indoor and outdoor PAHs pollution.