Forty-eight daily time interval PM_(2.5) samples were collected from December 2006 to January 2008 in an urban site in Shanghai, China. Concentrations and compositions of polycyclic aromatic hydrocarbons (PAHs) were analyzed with GC-MS to study the dial and seasonal variations and to identify the main emitting sources. The dial variation of the PAHs concentrations was greater in the late autumn and winter sampling days, and was greatly influenced by meteorological conditions such as wind speed and ambient temperature. The concentration of PAHs in the mings (6:30-10:00) increased distinctly, and was high in the late autumn and winter sampling days, indicating the contribution from vehicle emissions during rush hours. The dial variation of the high molecular weight PAHs did not seem to be controlled by the shift of gas-particle partitioning due to temperature variation, instead, it could be indicative of the variation in the source. Statistical analyses showed that the concentrations of PAHs were negatively correlated with temperature and wind speed, and positively correlated with relative humidity. Diagnostic ratios of PAHs suggested mixed emission sources of petroleum and coal/biomass combustion for PAHs in the PM_(2.5) in Shanghai.