and 6% Eucommia leaf powder was added to carp's feed which carp fed on for 30 days.The weight of carps and the relative percent survived after challenged with live Aeromonas hydrophila were determined.21 days after the inoculation with formalin killed Aeromonas hydrophila(F AH),the agglutinating antibody titer of serum and the phagocytic activities of leueocytes in the blood of every experimental group and control group were examed to determine the effects of Eucommia leaf powder on carps' immunization. The results showed that adding Eucommia leaf powder to carp feed promotes the immunoresponse level and growth strengthens their resistance against bacterium, especially the 4% and 6% Eucommia leaf powder.