For the last decades global climate changes, industrial development and growth of population in coastal cities led to changes of coral reef ecosystem. These changes are often negative. They appear as reef degradation. In 2010 the authors found the coral reef Sannest Islands, located not far from Cam Ranh city in East Vietnam Sea. The authors were impressed by coral species and other associated organisms abundance of the reef, which made it different from other nearly islands. That's why the authors studied the species composition and structure of this reef adjoining to the biggest island - island Hon Noi. In the work scuba technique and standard hydrobiological methods of frames and transects were used. the authors took pictures of underwater landscapes and reef inhabitants as well (more than 900 pictures). 282 species of macrophytes and invertebrate were found on the reef of the Hon Noi Island. 169 species were scleractinians. The following 27 species dominated: macrophytes Padina australis, Halophyllia ovalis, alcyonarian Sinularia dura and Sarcophyton trochelioforum, scleractiriian Acropora microphthalma, A.nobilis, A. valenciennesi, A. verweiy, Montipora aequituberculata, Mhispida, Mgricea, Hydnophora rigida, Porites cylindrica, P.rus, Platygyra daedalia, Leptoria phrigia, Favia speciosa and Favia sp., mollusks Tridacna maxima, T.crocea, T.squamosa, Lambis chiragra, echinodermata Diadema setosum, Holothuria atra, Slihopus chloronalus, Linckia laevigata and Ohpiocoma nigra. Monospecific settlements of up to 100m2 formed Acropora microphthalma and A. nobilis. These two species together with H rigid a, M aequituberculata .and M gricea formed dense settlements, totally covering big areas of the bottom. In total the coral species diversity of scleractinians was 27.4.