Concentrations of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured in Tianjin during January, April, July and October in 2008. The 24-h PM2.5 (particles with aerodynamic diameters less than 2.5 micrometer [μm]) and PM10 (particles with aerodynamic diameters less than 10 micrometer [μm]) samples were simultaneously collected every day during sampling periods. These samples were analyzed for OC/EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. The annual average concentration was 109.8 ± 48.5 μg/m3 in PM2.5, and 196.2 ± 86.1 μg/m3 in PM10, respectively. The average ratio of PM2.5/PM10 was 57.9%, indicating the PM2.5 had been one of the main contaminations affecting urban atmospheric environmental quality in Tianjin. The concentrations of OC and EC in PM2.5 and PM10 were all relatively higher in winter and fall and lower in summer and spring. This seasonal variation could be attributed to the cooperative effects of changes in emission rates and seasonal meteorological conditions. The annual average concentration of the estimated secondary organic carbon (SOC) was 14.9 μg/m3 and occupied 61.7% of the total OC in PM2.5, while those in PM10 were 23.4 μg/m3 and 61.2%, respectively, indicating SOC had been an important contributor to organic aerosol in Tianjin. The distribution of eight carbon fractions (OC1, OC2, OC3, OC4, EC1, EC2, EC3 and OP) was also reported and found that the biomass burning, coal–combustion and motor-vehicle exhaust were all contributed to the carbonaceous particles in Tianjin.