Suspended sediment samples were collected from the high-turbidity Shuangtaizihe estuary to analyze particulate organiccarbon (POC) and stable carbon isotope composition (δ13C) of organic materials. The POC values of the Shuangtaiziheestuary are relatively low (1.2-1.4%) but remain stable over the whole salinity range sampled, which suggests thepredominance of a terrigenous source over the mass transport of organic materials in the estuary. The δ13C values ofparticulate organic materials (-25.0 to -23.5%) are heavy compared to detritus of higher plants (e.g. tree leaves), butsimilar to other Chinese rivers. The compositional characteristics of POC and δ13C indicate a large and isotopically constantmaterial source from the organic matter reservoir of soils over the drainage basin.