Mangrove systems are known for high productivity from primary producers, which may have a significant impact on carbon cycling in the coasts and the carbon flux to the ocean. In order to evaluate the lability (more labile or more refractory) of mangrove-exported organic carbon, we studied the particulate organic carbon (POC) in a mangrove system and the nearby river stream from the Southeast of China, by using amino acids (AA) to represent labile particulate organic carbon (LPOC), and the rest part beside AA to represent refractory particulate organic carbon (RPOC). LPOC accounts for ~15% nearby the mangrove (W1 and W2) and ~20% in upstream stations (W9 ~ W12), indicating a major portion of the exported POC is subject to relatively slow turnover in the mangrove adjacent waters. Samples collected from W1 and W2 show higher differences between wAA δ¹³C and bulk δ¹³C than from W9 to W12, also supporting a larger portion of mangrove-derived RPOC. Besides, principal component analysis (PCA) of amino acids δ¹³C from different samples indicates that phytoplankton contribute more LPOC than the mangrove system. This research suggests that mangrove system might be a source of RPOC to the nearby river, indicating the potential of refractory organic matter to be transported from mangrove system to the coastal ocean.