【Objective】Organic matter in soil aggregates (POM, particulate organic matter) is a biologically and chemically active fraction of soil organic matter that plays an important role in terrestrial carbon cycling. The objectives of this study were to characterize the fraction of organic matter and to analyze stability and sources of the soil organic carbon pool in this study area. 【Method】 Soil samples were collected from three tracts of land typical of the studied region in land use, that is, barren land, saltmarsh and upland, for analysis of POM and stable organic carbon isotopes. 【Result】Results show that the content of soil organic carbon presented a curve of first rising from barren land to saltmarsh and then declining from saltmarsh to upland, and was found in a significant positive relationship with the content of soil macroaggregates. The organic matter in soil aggregates could be fractionated into free particulate organic matter (fPOM) on the surface of macro- (micro-) aggregates, intra-macro- (micro-) aggregate particulate organic matter (iPOM, 250~2 000 μm) and mineral-associated soil organic matter. Contents of fPOM, iPOM and mSOM (Mineral-associated Soil Organic Matter) were quite low in the barren land, but soil organic carbon content increased significantly in the three types of SOM in the saltmarsh where some halophytes began to grow, reaching as high as 410.0 g•kg^-1, 98.8 g•kg^-1 and 18.8 g•kg^-1 respectively. When saltmarsh was reclaimed into upland, the rising trend of the three types of POMs leveled off. The POM (including fPOM and iPOM) accounted for only 20% or below of the organic carbon in the barren land, for 41.8%~75.2% in the saltmarsh that had some halophytes growing, and for 54% in the upland. In terms of δ¹³C, the three types of POM exhibited an order of fPOM < iPOM < mSOM, and the three tracts of lands did an order of saltmarsh < upland < barren land. 【Conclusion】 All the findings in this study demonstrate that although the content of total soil organic carbon is relatively lower in the barren land in the Yellow River Delta, it has a relatively stable carbon pool consisting mainly of mineral-associated organic matter, which is highly affected by marine originated organic carbon. The growth of halophytes in the saltmarsh (wetland) increases the content of total organic matter in the soil and its relative proportion in the active carbon pool, too. Soil organic carbon pool is very sensitive to changes in environment. Cultivation of corn and wheat lowers the relative proportion of active carbon pool, but enhances stability of the so carbon pool.