Abstract: The present study was carried out on antimicrobial properties of seagrass species against biofilm forming bacteria’s from boat hull during the period April 2008 to March 2009. Seagrass species have a very potential groups were producing several secondary metabolites. The bioactive potential of two different seagrass species viz., Cymodocea serrulata and Syringodium isoetifolium occurring commonly along the Tuticorin coastal area were selected and preliminary effort has been made against the marine biofilm forming bacteria’s Pseudomonas aeruginosa, Bacillus cereus, Proteus vulgaris, P. mirabilis, E. coli, Listeria monocytogenes, Salmonella enteritidis, Staphylococus aureus and Vibrio paraheamolyticus, which also the human pathogens. The seagrasses of C. serrulata and S. isoetifolium were extracted with four different solvents such as ethanol, methanol, acetone and dichloroethane. Ethanol and methanol extracts of S. isoetifolium was inhibited the biofilm forming bacteria such as E. coli (14 mm), P. aeruginosa (8 mm) and V. paraheamolyticus (7 mm) and it showing Minimum activity against S. aureus (2 mm). The crude extract of ethanol and methanol of C. serrulata was inhibited the growth of all the 9 species of the biofilm forming microbes. The results of present study were concluded that seagrasses have potential bioactivity against marine biofilm forming microorganisms.