In order to sample, identify and determine Seaweed biomass in the Oman Sea coast (Sistan & Baluchestan Province) with 300 Km length from Gwatr area (with 25 10 N & 61 30 E) to Mydani (25 24 N & 59 5 E) during two years (from Octobr 2001 to September 2003), eleven regions of Gwatr, Passabandar, Beris, kachoo, Ramin, Chabahar, Pozm, Gurdim, Tang, Jood and Mydani were selected as sampeling stations from east to west. Seaweed growth area in intertidial zones determind by measuring and recording of geographic positions by metertape and GPS, then with the help GIS system and satellite maps, area, situation and maps of survey areas, were obtained 15 transects were determind with equal distance in coast area and monthly sampling were done randomly by quadrate 50*50 Cm the samples were transfered to the lab and the weight of each species was obtained after being cleaned, and separating. The biomass of each species per area unit and in the total area was obtained after determing the average weight of species. Also the prefered zones of each species were determined through the maximum number of presence in the transects. Along with this research, the Seaweed species were reconized according to the present references. The photographs were taken and the herbarium sheet was obtained. The samples were sent to experts for final approval. To compare the biomass changes during two years (2002 & 2003), this research was with the same methods of first year from October 2002 to September 2003 in Gwatr, Beris, Ramin, Tang and Jood. During this research 180 species were collected. Among these seaweeds, 160 species (composed of 39 species green algea, 39 species brown algae and 82 species red algae) were identified. There were some important families including green algae (Ulvaceae & Caulerpaceae), brown algae (Sargassaceae & Dictyotaceae) and red algae (Gracilariaceae, Gelidiaceae and Hypneaceae ). Wet biomass of Seaweeds in the total area of Sistan & Baluchestan coasts were 10269399 kg in 2002. Among this biomas, 2645223 kg (%25.7) green algae, 2953279 kg (%28.8) brown algae and 4670897 kg (%45.5) red algae were estimated and the monthly average for then were obtained 264522.3 kg, 295327.9 kg and 467089.7 Kg respectively. The maximum biomass was obtained 922246 kg in Chabahar and minimum biomass was obtained 1418 kg in pozm. The amount of alginophyte (Sargassum Spp.), agarophyte (Gracilaria, Gelidium & Gelidiella) and karaginophyte (Hypnea musciformis) were 159777 kg, 806915 kg and 188783 kg respectively. In second year (2003), the biomass of wet weight was 4114655 kg in 5 zones. Among this biomass, 849227.5 kg (%20.6) green algae, 1669792 kg (%40.6) brown algae and 1595636 kg (%38/8) red algae were obtained. The monthly average were 70769 kg, 139149.3 kg and 132969.7 kg respectively. The biomass of alginophyte, agarophyte and karaginophyte were 163776.4 kg, 481642.6 kg and 64310.1 kg respectively this year. Iranian Fisheries Science Research Institute Published