This study, represented by seaweeds growing on the Warambadi seashore of Sumba Island, has therefore the following primary purposes: to screen and to evaluate the antibacterial activities of selected red, green, and brown seaweeds; to isolate and to identify the compounds from active extracts from representative species of red, green, and brown seaweeds; and to evaluate the bio activities of the isolated compounds by antibacterial bioassays. Based on the above experimental problems, the following hypotheses are put forward : (a) seaweeds from Warambadi seashore of Sumba island contain secondary metabolites as bioactive substances; (b) extracts of those seaweeds have potentials against bacteria; (c) according to the classes of seaweeds, those seaweeds have diversity of secondary metabolites both in kinds and in molecular structures; (d) the single compounds of those secondary metabolites are bioactive substances as antibacterial; (e) there is a synergism among single compounds of those secondary metabolites as bioactive substances.