The survivorship and activity of lysozyme, phenoloxidase, superoxide dismutase, alkaline phosphatase and acid phosphatase in hemolymph of “Huanghai No. 1” and wild population of Fenneropenaeus chinensis,when they were exposed to different concentrations of Ammonia N,were studied. The result showed that the 24hLC50, 48hLC50, 72hLC50 and safe concentration of “Huanghai No. 1” were higher than the wild population. When ammonium chloride was 8 mg/ L in the culture system, the alkaline phosphatase and acid phosphatase activities of “Huanghai No. 1”were much lower than the wild population of F. chinensis (P<0.01). When the concentration of ammonium chloride was 16 mg/ L in the culture water, lysozyme activity of “Huanghai No. 1”was higher than the wild population (P<0.05) and alkaline phosphatase and acid phosphatase activity of “Huanghai No.1”was lower than the wild population (P<0.05). When the concentration of ammonium chloride was 32mg/ L in the culture water, lysozyme and phenoloxidase activity of “Huanghai No. 1” was much higher (P<0.01) and superoxide dismutase activity of “Huanghai No.1”was higher (P<0.05) than the wild population, and phosphatase and acid phosphatase activities of “Huanghai No.1”were lower than the wild population (P<0.05). When the concentration of ammonium chloride was 64mg/ L in the culture water, superoxide dismutase activity of “Huanghai No.1”was much higher than the wild population (P<0.01). When the concentration of ammonium chloride was 128mg/ L in the culture water, there were no obvious differences between the two populations. It was suggested that the anti disease ability of selected “Huanghai No.1” was better than the wild population at a range of low concentrations of Ammonia-N.