This experiment was conducted to study the effects of methionine on immune response and disease resistance of juvenile Jian carp (Cyprinus carpio var. Jian). Eight hundred sixty-four juvenile Jian carp with an initial body weight of (12.34±0.02) g were randomly allocated to 6 groups with 3 replicates each and 48 fish in each replicate . Methionine supplemental levels in the diets of 6 groups were 0.39%, 0.70%, 1.00%, 1.30%, 1.60% and 1.90%, respectively. After 60 days of feeding, a challenge trial was conducted by injection of Aeromonas hydrophila for 17 d to study the effects of methionine on immune function of juvenile Jian carp. The results indicated that suitable methionine levels in diet could significantly improve the head kidney index, hind kidney index, spleen index, erythrocyte and leukocyte counts and erythrocyte count post challenge (P<0.01); significantly elevate the leukocyte phagocytosis rate in growth trail, and significantly increase the survival rate, leukocyte count, leukocyte phagocytosis rate, acid phosphatase activity, lysozyme activity, complement component C3, agglutinin level in plasma and antibody titers after injection with Aeromonas hydrophila (P<0.05). In summary, methionine could improve nonspecific and specific immunity in juvenile Jian carp by enhancing the phagocytic activity of leukocyte and increasing Aeromonas hydrophila antibody titer, and subsequently elevate the disease resistance.