A　water-soluble　polysaccharide　WPS-2-1,　purified　from　Laminaria　japonica,　has　been　found　to　have　antitumor　activity.　In　this　study,　WPS-2-1　exhibited　high　anti-proliferative　activity　on　A375　cells　in　a　dose-dependent　manner.　Further　investigation　indicated　that　WPS-2-1　induced　A375　cells　apoptosis.　Moreover,　WPS-2-1-induced　apoptosis　was　associated　with　the　alteration　in　expressions　of　Bcl-2　family　proteins.　Mitochonadrial　apoptotic　pathway　was　involved　in　WPS-2-1-induced　apoptosis,　which　included　the　loss　of　mitochondrial　membrane　and　activation　of　caspase-3/9.　The　results　in　this　study　suggested　that　WPS-2-1　could　effectively　inhibit　proliferation　of　A375　cells　in　vitro　and　induce　apoptosis　via　mitochondrial　apoptotic　pathway.　It　might　serve　as　a　potential　antitumor　agent.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.