Abstract: Particle matter (PM) has become the primary air pollutant in Nanjing, recently. Investigation on particle matter source apportionment using Chemical Mass Balance(CMB) model could provide a theoretical basis for air quality management and air pollution control for the city. In this paper, the characteristics of PM2.5 chemical composition at Caochangmen (CCM) and Guchenghu (GCH) in Nanjing at 2011.8, 2011.11, 2012.1, 2012.3, respectively and atmospheric PM emissions samples were analyzed. Results indicate that four months average concentrations of PM2.5 at CCM and GCH are 100.9±45.2μg/m3 and 85.4±37.8μg/m3, respectively. The mass concentrations are both lowest in August. They are 82.7μg/m3 and 50.4μg/m3, respectively at CCM and GCH. PM2.5 of CCM is the highest in March with the average concentration reaching 134.7μg/m3. The highest value of PM2.5 at GCH was found in January reaching 94.3μg/m3. The main chemical compositions of PM2.5 are NO3-, SO42-, OC, NH4+, EC, Ca, Cl-, K, Fe, Al and Na. The major emission sources are coal dust, smelting dust, soil dust, vehicle exhaust, secondary aerosols and sea salt. Results from source apportionment show that in fine particulate matter, the sources with large contribution are the secondary inorganic aerosols (63.9%, 65.1%) and vehicle exhaust (12.5%、16.5%) at CCM and GCH, respectively. Therefore, in order to reduce the PM2.5 level in Nanjing, it is necessary to control emissions from industry and transportation.