Abstract: Amino acids are important biogenic organic matter and play a critical role in biogeochemical cycling of organic carbon and organic nitrogen in the ocean.As one of the most labile fraction of marine organic matter, amino acids can be selectively removed by heterotrophic bacteria during the organic matter degradation, and be considered as a sensitive indicator for the degradation of organic matter.In this paper, the classification of amino acids in seawater is introduced, and the reactivity of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), particulate amino acid (PAA) as well as the source of the D-amino acids are summarized.The changes of amino acids in the degradation process of organic matter can be ascribed to three mechanisms including selective preservation, production or enrichment of bacterial organic matter and transformation by the bacteria.Finally, comparisons of the characteristics, suitable degradation stages and specific applications of the six degradation indices including carbon-and nitrogen-normalized yields of total hydrolyzable amino acid (THAA-C% and THAA-N%), degradation index (DI), reactivity index (RI), the D/L-amino acid ratio, aspartic acid/β-alanine and glutamic acid/γ-aminobutyric acid ratios (Asp/β-Ala or Glu/γ-Aba) and bacterial contributions are summarized.