Abstract In this study the distribution of the sea grass located at the South Marmara Group Islands was observed. These species which are under the protection are also important in terms of being oxygen source and the biological diversity. There is a relation between the protections of the sea grass and the biological diversity of the sandy areas. This area was preferred since it has an important role in sea products. The results of this study could be used in the future researches. The most frequently observed sea grass species was Cymodocea nodosa that are widely distributed at sand banks around the archipelago. Upper limit of C. nodosa meadows was ~ 1 m, while the densest structure was encountered at 6-7 m depth. Zostera marina was detected more frequently at sandy substratum of Pa~alimaUl Island and Araplar location of Av~a Island. Posidonia oceanica distribution, on the other hand, was limited to a very narrow area at Harmanlar location of Pa~alimam Island. This is the first record of Posidonia at the Sea of Marmara. The presence of an isolated, small community at the region is very important since Posidonia is an endemic Mediterranean species and it is also very important to investigate spatiotemporal changes in distribution of the species at the basin. Recent diving surveys (August, 2004) showed the continuity of the community. This is the first record of the Posidonia oceanica existence in the Sea of Marmara in 1986-2004.