Abstract: In this study, total organic carbon (TOC), total nitrogen (TN), biogenic silica (BSi) and carbon stable isotopes (δ¹³C) of surface sediments were investigated in the Chongming Dongtan mudflats in summer 2019, aiming to examine the spatial distributions, sources and influencing factors of organic matter. Meanwhile, relationships between organic matter and macrobenthos distributions were also discussed. The results showed that the content of organic matter was higher in the northern part of the Dongtan and lower in southern part. The organic matter was constituted of marine organic matter, terrestrial organic matter and C₃ vegetation in the salt marsh, accounting for (35.22±9.20) %, (34.45±4.87) % and (30.33±4.34) %, respectively. The contributions of benthic diatom to the organic matter in mudflats are higher compared to that in the vegetation zone. Grain size is the most important factor affecting the spatial distributions of the organic matter in mudflats, however, the close values of δ¹³C between C₃ salt marsh and terrestrial organic matter may obscure the spatial difference of organic matter sources. The spatial distribution of the abundance and biomass of macrobenthos is significantly correlated to the organic matter contents, indicating that organic matter in surface sediments provides food basis for consumers. Our results support the understanding of the biogeochemical cycle of organic matter and the function of the food web in mudflats in data and references.