A　water-soluble　crude　polysaccharide　(WPS)　was　obtained　from　Laminaria　japonica　by　hot　water　extraction.　Three　major　polysaccharide　fractions　(WPS-1.　WPS-2　and　WPS-3)　were　purified　from　WPS　by　anion-exchange　chromatography.　Monosaccharide　components　analysis　indicated　that　galactose　was　the　predominant　monosaccharide　in　WPS　and　WPS-3,　accounting　for　56.25%　and　54.11%,　respectively.　And　fucose　was　the　predominant　monosaccharide　in　WPS-1　and　WPS-2,　accounting　for　46.91%　and　45.1%,　respectively.　Antioxidant　activity　tests　revealed　that　WPS-2　showed　significant　function　of　scavenging　hydroxyl　free　radical　and　WPS-1　exhibited　the　highest　inhibitory　effects　on　superoxide　radical.　Cytotoxicity　of　all　polysaccharide　fractions　was　evaluated　by　MTT　assay　and　Hoechst　33258　staining.　Results　showed　that　WPS-1　and　WPS-2　significantly　inhibited　the　growth　of　A375　cells　and　low　anti-proliferative　effects　of　WPS-2　on　vascular　smooth　muscle　cells　(VSMCs)　were　observed.　These　results　suggested　that　the　polysaccharide　fraction　of　WPS-2　might　be　explored　as　a　potential　safe　antioxidant　and　antitumor　agent.　(C)　2012　Elsevier　B.V.　All　rights　reserved.