Abstract: The silver crucian carp)Caressius auratus gibelio)were immunized with crude lipopolysaccharide(LPS)extracted from Cytophaga columnaris、Aeromonas hydrophila and Vibrio anguillarum .The relative percent survival(RPS)of silver crucian carp were compared by examing the agglutinating antibody titers,cross agglutinating antibody titers of serum and the phagocytic activity of phagocytes in the blood and head kidney challenged with live A. hydrophila .The experimental results showed that the agglutinating antibody titers and cross agglutinating antibody titers of immunized silver crucian carp were higher than the control group,and the phagocytic activity of phagocytes in the blood and head kidney of silver crucian carp was significantly boosted and had a high level cross RPS.The crude LPS of three pathogenic bacteria were thought to have a common protective antigens to causing a cross RPS to silver crucian carp.