The exopolysaccharide from Bacillus marinus is of study interest due to its wide spectrum bioactivity and high production (8.2g/L), so the strain isolated and identified based on morphological and characteristics. The EPS was obtained through the ethanol precipitation from fermentation broth and fractionated by anion-exchange and gelfiltration chromatography. The main fraction of EPS (BMEPS) was determined as homogenous with a molecular weight of 500 kDa. Its structural characteristics were investigated and elucidated by periodate oxidation, Smith degradation, HPLC, FT-IR. It was contained sulfate group (20.2%) and composed of glucose and glucouronic acid in a molar ratio of 3:1, respectively. Small amount of glycerol and large amount of liberated erythritol partially prove the presence of the β-(1−4) linkages between the monosaccharides in the backbone of the polysaccharide. The chemical analysis showed that the proposal structure could be as [Glc-β-(1−4)-Glc-β-(1−4)-Glc.A]n. The biological activities of crude EPS and BMEPS as antiviral against MDCK and H1N1 virus and antioxidant were done. In addition, the antitumor against human breast adenocarcinoma cell line (MCF-7) and human alveolar basal epithelial cell line (A-549) was evaluated by MTT assay. The results suggested that F-6 could be considered as an effective natural antiviral, antioxidant and antitumor sources.