Abstract: According to the Stoke's Law, the grain sizes of sediments from the Yangtze River and the Yellow River are classified into four and six grades, separately. The REE contents in the sediments of various sizes are tested with ICP-MS. The results show differences between the two rivers. For the same grain size, the content of REE in the samples form Yangtze River is higher than that from Yellow River. The contents of REE form the Yangtze River reduce with the increasing of grain sizes of sediments. However, with the increasing of grain sizes, the REE contents in samples from the Yellow River present an unsymmetrical high-low-high distribution pattern. The North America Shale-normalized patterns show that the fractionation patterns are similar for different grain-sized sediments, and also for the two rivers. The differences of REE contents between the Yangtze River and the Yellow River are closely related to the weathering and mineral compositions in the sediments of the two river basins. The reducing trend of REE contents with grain size increasing for the Yangtze River is resulted from the dilution of quartz and feldspar contents which increase with the grain size. The REE distribution pattern of sediments from Yellow River is the result of the absorption of clay minerals in fine-grained sediment and the enrichment of heavy minerals in coarse-grained sediment.