Phytochemical investigation of leaves of Brownlowia tersa, a Shurb from Sundarbans(the largest Mangrove Forest of the World); indicated the presence of Reducing Sugars, Glycosides, Saponins, Tannins & Flavonoids types of compounds. The extract was assessed using brine shrimp lethality as an ndicator of toxicity & showed significant level of toxicity (LC50=10µg/ml & LC90=86µg/ml). The antibacterial activity of the extract was investigated, using disc diffusion method which showed antimicrobial activity against some gm(+) & gm(-) bacteria such as Staphylococcus epidermidis , Vibrio cholerae, Streptococcus agalactiae , Shigella sonnei, Streptococcus pyogenes, Staphylococcus saprophyticus, Staphylococcus aureus at the dose of 500µg/disc.