Seaweeds form an important renewable source in the marine environment and have been known as a source of natural nutritive compounds such as free amino acids. For that purpose, this study aimed to investigate the amino acids contents of some brown (Cystoseira trinodis, Saragassum muticum, and Turbinaria ornata), red (Laurencia papillosa, Jania rubens, and Coralina officinalis), and green seaweeds (Caulerpa racemose, Ulva lactuca, and Halimeda tuna). Amino acids were analyzed using an LC 3000 eppendorf / Biotronik amino acid analyzer. Results revealed that the total amino acid content ranged from 11.84 ± 0.55 mg g-1 DW in L. papillosa to 33.43 ± 1.29 mg g-1 DW in U. lactuca. L-methionine and threonine were the major essential amino acids (EAAs) in Phaeophyta, and Chlorophyta species, respectively, whereas in Chlorophyta species, the major EAA was varied as L-lysine, L-leucine, and L-valine in C. racemose, U. lactuca, and H. tuna, respectively. In all the tested species, L-glutamic and L-aspartic acids constituted together a large part of the amino acid content forming 16.3 - 34.8% of total amino acids. Among the nine seaweeds, U. lactuca contained the highest amounts of EAAs (17.4 ± 0.73 mg g-1 DW). The amino acids compositions of seaweeds are highly influenced by seaweeds classes and species. The high content of EAAs in the tested species made them candidates for nutritional and pharmaceutical applications.