We studied the organisms attached to Sargassum beds in Gamak Bay from November 2007 to June 2008. The water temperature ranged from 3.3 to $28.7^{circ}C$ and salinity from 30.6 to 33.8 psu. Eighteen species $143,432;ind./m^2$ were sampled during study periods. The biomass of the Sargassum beds ranged from a highest of $196.08;g;dw/m^2$ in March to a lowest of $0;g;dw/m^2$ in July. The major dominant species were Barleeia angustata ($134,430;ind./m^2$), Caprellidae sp.($2,443;ind./m^2$) and Gammaridae sp.($4,201;ind./m^2$). The ecological indices of diversity, evenness, and richness were 0.11-0.86, 0.04-0.39, and 0.74-1.06, respectively.