Sargassum C. Agardh (Sagassaceae, Phaeophycaeae) is a brown algae in the Iranian southern coasts which they showed high density along the subtidal zone of area. In this study, the features of four species of Acanthocarpicae (S. crassifolium J. Agardh and S. oligocystum Montagne) and Malacocarpicae (S. baccularia (Mertens) C. Agardh, S. henslowianum C. Agardh) were described. Species within the Malacocarpicae section were typified by having smooth receptacles, whereas those in the Acanthocarpicae section had spiny receptacles. Also, presence of discoid to conical holdfast, elongated to lanceolate leavesand with wavy to denticulate margin were the main characters of these sections. S. baccularia was characterized by less sping branches compared to other species. S. crassifolium and S. oligocystum had flattened primary branches, their leaves mostly wavy or denticulate at margins, with leaf-like mucronate at vesicles apex and racemose to paniculate receptacles.