Abstract: Marine biofouling causes a lot of damage to the shipbuilding and aquaculture industry because of the increasing maintenance costs. The purposes of this research are to measure the effectiveness of seaweed to inhibit bacterial biofilms and determine their inhibitory concentrations. In this study, we used Sargassum polycystum and Ulva reticulata from Punaga coast, Takalar South Sulawesi, extracted with methanol to determine the potential of the extract as