In the South China Sea region, members of the Sargassaceae are the largest seaweeds and are of economic value in the industries. On the extensive reefs around the Xisha islands, there are several species of this family which are present in large quantities. In the present study a taxonomic study of five species of Xisha Sargassum was made. Two new species were reported, namely S. subtilissimum and S emarginatum.