The purpose of the research was to analyze bacterial activity from methanol extract of Halodule UninervisagainstGram-negative bacteria (Aeromonas hydrophila and Vibrio harveyi) and Gram-positive bacteria (Bacillus subtilis and Listeria monocytogenes).The result showed content of phenolic was 20.17ppm and content of tannin was 1,223 ppm.Antibacterial activity of an extract showed that seagrass can inhibit several types of Gramnegative bacteria (Aeromonas hydrophila and Vibrio harveyi) and Gram-positive bacteria (Bacillus subtilis and Listeria monocytogenes). As for the highest inhibitory activity present in the type of Gram-positive bacteria (Bacillus subtilis and Listeria monocytogenes) between 7 mm to 9 mm.
