Abstract: The distribution and composition of total hydrolyzed amino acids (THAA), dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA) were analyzed in the seawater samples collected at 43 stations located in the East China Sea and the Yellow Sea in March 2011. The results showed that the average concentration of THAA in the surface water was 2.981.72 mol/L (in the range of 1.27 to 8.54 mol/L), while the average concentrations of DCAA and DFAA in the surface water were 2.761.63 mol/L (in the range of 0.91 to 7.70 mol/L) and 0.310.21 mol/L (in the range of 0.11 to 1.14 mol/L), respectively. The concentrations of dissolved amino acids displayed a decreasing trend from inshore to offshore stations, especially DCAA and THAA. In the vertical distribution, the high values of THAA appeared in the subsurface layer and in the bottom layer of the water column. In the study area, major constituents of dissolved amino acids were aspartic, glycine, serine, glutamic acid and alanine acid. Correlation matrix analysis of amino acids indicated that 5 pairs of amino acids in DFAA showed significant positive correlations. No significant correlations were found between the concentrations of dissolved amino acids and environmental factors such as chlorophyll a, dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN).