Mauran (MR), a highly polyanionic sulfated exopolysaccharide was extracted from moderately halophilic bacterium; Halomonas maura and characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Purified MR was evaluated for antioxidant defense mechanisms under in vitro conditions using L929, mouse fibroblast cell line and mice liver homogenate. It was demonstrated that MR could impart protective effect against oxidative stress in both cells and tissue up to a concentration of 500 μg, which is found to be safe under laboratory conditions. Various enzymatic and non-enzymatic parameters of antioxidant mechanisms were evaluated and concluded that MR has the tendency to maintain a balance of antioxidative enzymes with in the test systems studied. Also, hemocompatibility assay performed revealed that MR has a lesser hemolytic index and exhibited a prolonged clotting time, which shows both antihemolytic, and antithrombogenic nature respectively. Furthermore, absorption studies performed using fluorescent-labeled MR confirmed that MR accumulated within the cell cytoplasm neither induced cellular lysis nor affected the cell integrity.