The　bioactive　of　polysaccharides　have　relationship　with　their　molecular　weight　Agarcus　blazai　Murill　(ABM)　polysaccharides　were　extracted　by　membranes　technology,　and　were　graded　according　to　the　molecular　weight　using　the　combined　method　of　microfiltration　(MF),　ultrafiltration　(UF)　and　nanofiltration　(NF)　membrane　modules.　The　effect　of　gradation　were　indicated　by　the　high　performance　gel　permeation　chromatography　(HPGPC),　and　lymphocyte　proliferations　in　the　different　molecular　weight　ABM　at　the　concentration　range　of　10-800　μ　g/ml　were　detected　with　MTT　method.　The　results　of　the　experiment　indicated　that　the　MF-UF-NF　combined　method　was　effective　for　ABM,　and　were　remarkably　shown　to　increase　lymphocyte　proliferation　at　100000Da　of　100,　200,　400,　300　g/ml　ABM　(p