Abstract: The relationsh ips of the ant-idisease ability of Litop enaeus vannam ei and the effects of biological control of bacteriophageto Vparahaem oly ticus were studied under different ammon ia conditions1T he 0.05mg/L, 0.15mg/L, 0.75mg/L,1.50mg/L and 3.00mg/L ammon ia nitrogen concentration gradients were des igned as amm onia stress expermi entgroups The V1parahaemolyticus was added into the ammonia stress expermi ent groups, the infection expermi ent groups were ga ined1The V1parahaemolyticus bacteriophage was added into the infection expermi ent groups, the bio-control experiment groupswere ga ined In the amm onia stress expermi ent groups, 0.05mg/L and 0.15mg/L ammonia n itrogen were added into the propheno oxidase(PO), superox ide dismutase (SOD), catalase hosphatase (CAT) and acid phosphatase(ACP) activit ies in the serum of L1vannam ei1But at the 14th, in a ll the ammonia stress expermi ent groups, the PO, SOD, CAT and ACP activit ies in the serum and the total haem ocyte count (THC) in the haemo lymph ofL1vanname iwere less than those in the 0.05mg/Lamm onia expermi ent group1The difference was s ignificant (p<0.05)In the infection expermi ent groups, the PO, SOD and CAT, ACP activities in the serum and the THC in the haem olymph of L1vannam ei were less than those in the amm onia stress expermi ent groups1The d ifference was s ignificant (p<0.05) Among the bio-contro lexpermient groups, in the 0.05mg/L and 0.15mg/L ammon ia stress expermi ent groups, the PO, SOD, CAT and ACP activit ies in the serum and the THC in the haemolymph ofL1vannamei were better than those in the infection expermi ent groups, the d ifference was s ign ificant (p<0.05), the V1parahaem oly ticus count in the haem olymph were less than those in the infection expermi ent groups, the difference was s ign ificant (p<0.05) 1A t the 14th, the PO, SOD, CAT, ACP activit ies and THC in the sam e groupswere smi ilar to those in the amm onia stress expermi ent group The resu lts show ed that the bacteriophage could controlV1parahaemolyticus well under low ammonia nitrogen concentration conditions