Derristrifoliata Lour.is a mangrove traditional plant in Fabaceae family which plays an important role in maintaining coastal ecological balance. Its leaves and barks were collected from Rajamangala beach, Rajamangala University of Technology Srivijaya, Trang province.Both parts were extracted according to polarity of hexane, ethyl acetate and methanol giving six fractions. Preliminary phytochemical screening of the dried leaf and bark extracts was investigated. Results revealed the presence of bio active substances such as anthraquinone, terphenoid, flavonoid, saponin, tannin, and alkaloid. The total phenolic content was evaluated by Folin-ciocaltue method. The results showed that methanolic leaf and bark extracts exhibited thehighest total phenolic content values 2.006±0.041 and 3.297±0.043 mg GAE/g extract, respectively corresponding to the presence of tannin in this plant. The antimicrobial activities of leaf and bark crude extracts were determined using paper disk diffusion method with gram positive and gram negative bacteria (Bacillus cereus TISTR 687, Staphylococcusaureus TISTR1466, Escherichia coli TISTR 780 and Salmonella typhi TISTR 292). Good activity was exhibited by methanol extracts of leaf and bark of the title plant. None part of this plant showed antibacterial activity to E. coli.