Five different type of seaweeds (Sargassum wightii, Padina tetrastomatica, Caulerpa racemosa, Agardhiella subulata and Stoechospermum marginatum) were collected from the Gulf of Mannar Coast and their antibacterial activities were screened against four pathogens namely Escherichia coli, Klebsiella pneumonia, Salmonella typhi and Vibrio cholerae. The zone of inhibition ranged between 9.2–1mm in methanol extract. The maximum activity (9.2 mm) was recorded from Agardhiella subulata and Stocheospermum marginatum against Klebsiella pneumonia and