Hemocytes of f reshwater mussel( Anodonta woodiana pacif ica) after injured in mantle were extracted from adductor, and the phagocytic activity against bacterium Pseudomonas f luorescens during 0- 25 days was studied in vitro assay. It was found that the granulocytes and agranulocytes of four type hemocytes had the ability of phagocytose. Phagocytic activity of hemocytes increased signif icantly f rom 10 days af ter mussel were injured, and came to the highest on 20 days, then reduced slowly. The serum from injured and control mussel showed an opsonization to the phagocytosis of hemocytes.