In order to explore the composition characteristics and distribution pattern of organic carbon (OC) in river sediments, river sediments and riverbank soils were sampled from upstream to downstream of the Majia and Tuhai rivers in northern China, and then determined for heavy fraction organic carbon (HFOC) and light fraction organic carbon (LFOC). Results showed that the HFOC had a significant correlation with LFOC in Majia riverbank sediments or soils, indicating that HFOC and LFOC might have homology and that the Majia River is relatively stable. The distribution pattern of OC is changing irregularly along with rivers. Mean HFOCs in sediments were slightly higher than that in riverbank soils in both studied rivers. Contributions of some other sources of OC that accumulated in sediments might result in better capacity of sediments to OC than soils of riverbank. Our study demonstrated that sediments could accumulate HFOC and LFOC derived from many sources, and had a better capability for the storage of OC, irrespective of HFOC and LFOC.