The objective of the present research aims to identify the distribution and sources of organic carbon in surface sediments of mangrove forests from Mui Ca Mau National Park using stable isotope analysis. Results showed that water content, LOI, TN, TOC and C/N ratios in surface sediments of the fringe mangrove forest were lower than those in surface sediments of the interior forest. In contrast, the bulk sediment density, δ13C and δ15N in surface sediments of the fringe mangrove forests were higher than those in sediments of the interior mangrove forest. The non-linear relationship between δ13C and C/N ratios indicated that sources of organic carbon in surface sediments of the fringe mangrove forest were mainly from tidal particulate organic matter and phytoplankton, the sedimentary organic carbon in the interior mangrove forests mainly originated from mangrove litters. The present study demonstrated that the distribution and sources of organic carbon in surface sediments of mangrove forests from Mui Ca Mau National Park are changed following the succession of mangrove forests and the distance from the river bank towards the interior mangrove forests. Results from present study will contribute the scientific fundamental for implementing the studies that aim to examine the ecological functions of mangrove forests in maintaining biodiversity of aquatic animals and to reconstruct the paleoenvironment in the mangrove intertidal zone using stable isotopes.