Seagrass study has been conducted in Tasik Ria waters in the district of the Minahasa area. The aims research is: 1. to know the physical and chemical conditions at the waters.2. To identify seagrass species found on research location and to study the community structure of seagrass. Four seagrass species have been found in the study i.e. Halophila ovalis, Enhalus acoroides, Thalassia hemprichii, dan Syringodium isoetifilium. The number of individuals of seagrass varied between 316 to 662, species densities were varied between (84.27-176.53/m²), relative densities were (16.06-33.62), index of occurrence were (0.1-0.4), the relative frequency was (10-41.66%), the dominance was (84.27-176.5), the relative dominance were (16.04-33.62%). Thalassia hemprichii has the highest on important value has Index of dominance was 0.265, while the diversity index was 1.354, and the distribution pattern was 1.028.