In recent years, atmospheric particulate matter has become the primary air pollutant in Nanjing, China. In order to support a scientific basis for particles reduction, it is of great importance to investigate the contribution of different sources to particulate matter. In this paper, the characteristics of chemical composition of observational data for size-fractionated particulate matter at Gulou site and Pukou site in Nanjing from May 2010 to April 2011 were analyzed. Emission samples of particulate matter were collected and size-fractionated particulate chemical compositions were analyzed to obtain the source profiles. A chemical mass balance (CMB) model was applied to apportion the contribution rate of different sources. Investigations show that the annual average concentrations of PM10 (particles with an aerodynamic diameter of 10 µm or less) at Gulou and Pukou are 135.8 ± 66.4 μg m–3 and 132.2 ± 73.0 μg m–3, respectively. For PM2.1, the concentrations are 55.1 ± 36.3 μg m–3 and 64.8 ± 40.2 μg m–3, respectively. The dominant chemical constituents are SO42–, NO3–, Ca, NH4+, Cl–, Fe, Al, and K, accounting for 93.02% and 91.56% of all of the measured compositions in PM10 at Gulou and Pukou. These components account for 95.23% and 93.48% of PM2.1 at Gulou and Pukou. Seven types of sources, including coal combustion dust, construction dust, smelting dust, soil dust, vehicle exhaust, secondary aerosols and sea salt, are considered. The results of source apportionment show that in coarse particles, construction dust contributes a maximum of 58.9% at Gulou and 47.3% at Pukou. Smelting dust, as the second most important source, contributes 14.1% and 19.7% at these two sites. For fine particulate matter, secondary inorganic aerosols and coal dust contribution are the two largest sources accounting for 58.8% and 15.9% at Gulou and 44.2% and 39.5% at Pukou. The findings will be useful for the local government to create efficient control strategies to reduce the emission of construction dust and to pay great attention to the prevention of secondary aerosols and coal combustion dust.