Abstract: Carbonaceous aerosols constitute major component of atmospheric aerosols. In Feburay, May, July and September of 2004, size resolved aerosol sampling measurements are conducted respectively at Shangdianzi Regional Atmospheric Background Monitoring Station which is in the suburb of Beijing, to represent the four seasons of the year. OC, EC are analyzed in the lab with Sunset OC/EC Analyzer (NIOSH TOT method, Sunset Lab, USA). The seasonal variations and size distributions of OC and EC composition are characterized, and correlations between OC and EC are discussed as well. The analysis shows that the mean concentration of OC for TSP (Total Suspend Particles) at Shangdianzi Station in the four seasons ranges from 7.5 μg·m^-3 to 31.5 μg·m^-3, and EC ranges from 1.4 μg·m^-3 to 6.6 μg·m^-3. As to PM_2.1 (particles with aerodynamic diameter less than 2.1 μm), the mean concentrations are from about 4.0 μg·m^-3 to 19.1 μg·m^-3 for OC, and from about 0.8 μg·m^-3 to 4.3 μg·m^-3 for EC. The significant seasonal variations of mean OC, EC at Shangdianzi are found with the highest OC and EC concentration appearing in winter and lowest in summer. The size distributions of OC and EC at the Shangdianzi Station shows obvious seasonal differences, with OC and EC peak size at 0.65—2.1 μm during the winter, summer and fall time, and shifts to 2.1—4.7 μm during the spring time. In summer and fall, the OC and EC are mostly concentrated in the fine particles (with particle size less than 2.1 μm). In spring, the size distributions of OC and EC are quite different, where there is a significant enhancement OC, EC mass contents in the coarse particles, which is related to the collision of carbonaceous aerosols with dust particles rich in the spring atmosphere. The mass of organic matter (OM=1.4OE) in PM_2.1 accounts for about 43%—80% of the total mass of OM, and EC in PM_2.1 accounts for 54%—70% of total EC. The average ratio of OC and EC for the whole period of sampling is about 4.0—6.0, which is similar with the reported values obtained at many urban sites of China, when considering the difference between the OC, EC laboratory analysis methods. The square correlation coefficients (R²) between OC and EC in winter, spring and fall are 0.84, 0.81, and 0.73 respectively. However, the correlation coefficient is lowest in summer, with R² about 0.49. This seasonal pattern of correlations indicates the complications for sources and production or removal processes of the carbonaceous aerosols in summer time in that region.