The marine macroalgae of Madagascar have been poorly studied, probably due to difficulties in accessing most of the 4,828 kms of coastline spreading across more than 14° of latitude. Recent collecting trips in the southern and northern sections of the island provided large collections to contribute towards a better knowledge of the marine macrophyte diversity of Madagascar. The present study focuses on the brown macroalgal genus Sargassum. Based on morphological and molecular analyses of the nuclear ITS2, chloroplastic partial RuBisCO operon and mitochondrial cox3 and 23S, we delineated a total of 11 taxa including seven new records (*) for Madagascar and an unidentified taxon: S. elegans*, S. ilicifolium, S. ilicifolium var. acaraeocarpum*, S. incisifolium, S. cf. latifolium, S. obovatum*, S. polycystum, S. portierianum*, S. robillardii*, S. swartzii* and S. sp In addition, nine taxa listed in the literature were not found during these recent collecting trips, implying a possible full list of 20 Sargassum species for Madagascar. More collections are required for a comprehensive revision of the Sargassum diversity of the island, particularly along its west and east coasts.