In this study, PM2.5 samples had been measured from the summer of 2009 to the winter of 2010 in a suburb of Shenzhen. The results indicated serious PM2.5 pollution in the suburb of Shenzhen. Seasonal and daily variations of water-soluble ions were discussed. SO4(2-), NO3(-) and NH4+ were the most abundant ions in winter. In summer, the average contributions of Cl(-), Na+, K+, Ca2+ and Mg2+ increased significantly, while SO4(2-), NO3(-) and NH4+ decreased. Furthermore, Naphthalene, acenaphthylene, acenaphthene and benzo fluoranthene were the major PAHs in PM2.5. Ratio analysis and characteristic compounds analysis were also used to determine the possible sources of PM2.5 in the suburb of Shenzhen.