Biofilm is a starting point of biofouling and biocorrosion. However, there was not enough information about the biofilm forming bacteria in marine environments. In the present study phylogenetic position and bacterial properties thought to be concerned in biofilm formation such as cell surface hydrophobicity, attachment ability on surface, production of quorum sensing (QS) signal molecule etc. were investigated for 76 isolates of 3 days old biofilm. The isolates were able to be assigned to 28 known genera which have been reported widespread in marine environment. Approximately 31% of the isolates had been reported previously as uncultured or unidentified in GenBank database. Cell surface hydrophobicity and attachment ability were usually incompatible in a same strain except two isolates. Among the 39 strains produce QS molecule, 21 strains were able to degrade QS molecules. Strains showing same property were usually affiliated into same phylogenetic group. This result implied that the role of bacterial strains in the process of biofilm formation is closely related to the phylogenetic position. [Supported by NRL for HKLee]