Abstract: Chemical characteristics and possible sources of fine particular matter (PM2.5) was investigated for 1 year in Nanjing. PM2.5 was collected from June 2007 to May 2008, which carbonaceous species, organic carbon (OC) and elemental carbon (EC), in the samples were analyzed. Seasonal variations of OC and EC concentrations were investigated; the pollution degree and characteristics of carbonaceous aerosols during haze and no haze period were analyzed and compared. Results showed that yearly PM2.5 and carbonaceous concentrations varied in wide ranges with 12.1~287.1mg/m3 for PM2.5, 2.6~47.0mg/m3 for OC and 1.0~33.6mg/m3 for EC. On seasonal average, the highest PM2.5 (109.6mg/m3) and OC (20.8mg/m3) levels occurred during summer. The seasonal average concentrations of PM2.5 and organic carbon levels ranked by the order of summer > autumn > winter > spring, while the seasonal average concentrations of EC were in the order of autumn, spring, winter and summer. The OC/EC ratio and concentrations of carbonaceous species such as,OC, EC and total carbon (TC) in haze days were 1.7 2.0, 1.8, and 1.9 times higher than those in non-haze days. Backward air trajectories indicated that haze formation in Nanjing was attributable to air masses with abundant water vapors and pollutants.