Organic and elemental carbon (OC and EC) were measured in PM2.5 and PM10 at urban and suburban sites in Tianjin, China, from September 2009 to February 2010. Average PM2.5 and PM10 mass levels were 124 and 243 μg/m3, respectively, with 53% of the PM10 mass present as PM2.5. The average OC and EC concentrations in PM2.5 were 14.5 and 4.3 μg/m3, respectively, while those in PM10 were 33 and 6.1 μg/m3, respectively. Relation of OC and EC to the trace elements As, Zn, K and Pb and principal component analysis indicated that multiple sources contributed to the OC and EC. Secondary organic carbon was found to constitute 46% and 66% of the total organic carbon in PM2.5 and PM10, respectively, in autumn and 41% and 56%, respectively in winter.