Mass concentrations of PM2.5 and 20 polycyclic aromatic hydrocarbons (PAHs) were measured in 15 non-smoking residences in three residential buildings located in urban area of Guangzhou, China during the 15 continued clear days from November 1 to 15 in 2002. The indoor and outdoor concentrations of PM2.5 significantly exceeded the daily average concentration of proposed by USEPA, with ranges of 82.12– and 83.33–, respectively. The ∑PAH concentrations ranged from 14.18 to and 15.83 to in the indoor and outdoor samples, respectively, with 5–7-ring PAHs (from benzo[b]fluoranthene to coronene, MW=252–300) as the predominant contributors (79–90%). High positive correlations between indoor and outdoor concentrations of PM2.5 and PAHs, which were due to the high efficiency of indoor ventilation, indicated that concentrations of these indoor air pollutants were dominated by outdoor sources. The results of source identification indicated that vehicular emission was the major source of these pollutants with minor contributions from some non-traffic sources. The better linear regressions of BghiP than BaP to the total amount of the other 18 PAHs, as well as the more stable profiles of 11 carcinogenic PAHs with molecular weight from 228 to 300 relative to BghiP than to BbF, BkF, BeP, BaP, and IcdP indicated that BghiP might be used as a more valid indicator of PAHs in such heavily vehicle-polluted urban air as in Guangzhou. Site specifically, the highest concentration of PAHs was found in Building 1, next to the road with heavy traffic. Vertical distributions of outdoor and indoor PM2.5 and PAHs at Building 1 indicated that people breathing at different height were exposed to different concentrations of these health threatening air pollutants.