Durvillaea antarctica was extracted with hot water and a sulfate containing polymer was obtained after separation of laminaran and alginic acid with cetrimide and 2% calcium chloride solutions, respectively. Gel electrophoresis showed that the acidic polysaccharide (23.5% sulfate, 4.5% uronic acid) was not homogeneous. It was fractionated by anion-exchange chromatography on DEAE Sephadex with increasing concentrations of KC1 solutions affording seven fractions. All the fractions showed blood-anticoagulant activity. The fraction eluted with 1.2 M KC1 (34.85% sulfate, 1.4% uronic acid) showed the highest thrombin time. The plaque inhibition and the transcription assays of the whole acidic polysaccharide and the partial hydrolysis product against the infectious pancreatic necrosis virus showed a slight antiviral effect.