The Streptomyces sp. NS4-6 was isolated from mangrove sediments collected from Nakhon Si Thammarat. The total lipids of intra- and extracellular fractions were extracted by the Folch method and were classified by solid phase extraction technique (SPE).  Fatty acid compositions were analyzed by GC/FID. The lipid extracts were assessed antibacterial activity against three Vibrio species using disc diffusion and micro broth dilution techniques. The result showed that the extracellular extract exhibited antibacterial activity against Vibrio parahaemolyticus, V. alginolyticus and V. vulnificus with the MIC value of 128, 128 and 16 µg/ml respectively while the intracellular extract showed low    activity against V. vulnificus. The extracellular lipid extract consisted of saturated fatty acids (SFAs; 51.89%), mono-unsaturated fatty acids (MUFAs; 16.85%) and polyunsaturated fatty acids (PUFAs; 1.72% of total fatty acids) whereas PUFAs (39.01%) were found in higher amounts than SFAs (30.54%) and MUFAs (18.39%TFA) in intracellular lipid extract.