Disclosed are novel materials separated from Ecklonia cava, a method for extracting and purifying the same, and the use thereof for antioxidants. The method comprises extracting antioxidative ingredients from powdered Ecklonia cava one or more times with an organic solvent; fractionating the antioxidative ingredients one or more times in solvents; and purifying the solvent fractions by chromatography. Superior in scavenging activity and thermal stability, the extract from Ecklonia cava can be used as antioxidants and is suitable in commercialization.