Abstract: In order to have a deep and thorough understanding of sediment organic matter in mangrove wetland of the Pearl River Estuary, we analyzed the distribution, stocks and source of soil organic carbon (TOC) and total nitrogen (TN) of the mangrove wetland in Qi'ao Island. The results show that the TOC content in the surficial sediment of seven main mangrove communities (Kandelia candel, Sonneratia opetala, Aegiceras corniculatum, Bruguiera gymnorhiza, Acrostichum aureum, Acanthus ilicifolius, Excoecaria agallocha) was 1.125%−1.969%, and the TN content was 0.058%−0.136%. Among the seven main mangrove communities, K. candel had the highest TOC content of inner forest, while S. opetala had the highest TOC content of forest edge. The lowest TOC contents of inner and edge both appeared in B. gymnorhiza communities. Moreover, the TOC content of inner forest was always higher than that of edge. The C/N of the surficial sediment was 12.032−26.690, showing that higher plants have a higher contribution rate to its organic matter composition. According to the C/N bivariate mixture model, about 70.21% of TOC input came from endogenous input of vegetation. Affected by factors such as land use change, TOC and TN content fluctuated in 0−30 cm soil layer. The storage of organic carbon (SOC) was 56.83−69.54 t·hm⁻², showing the strong TOC storage ability of this mangrove wetland in Qi'ao Island.