Abstract: The current study explored the acute biological toxicity of ammonia-N on Palaemonetes sinensis. In the condition of (18±1)℃, pH 7.3±0.1, the half lethal concentrations of ammonia-N were 565.47 mg/L for 24h, 371.16 mg/L for 48h, 291.16 mg/L for 72h, and 272.50 mg/L for 96h, respectively, and the safe concentration was 27.25 mg/L. In the same condition, half lethal concentrations of non-ionic ammonia were 3.74 mg/L for 24h, 2.45 mg/L for 48h, 1.93 mg/L for 72h, 1.80 mg/L for 96h respectively and the safe concentration was 0.18 mg/L. Five different concentrations (60 mg/L, 100 mg/L, 140 mg/L, 180 mg/L and 220 mg/L) were used to study the influence of ammonia nitrogen stress on the non-specific immune indexes based on 96h LC₅₀ and safety concentration. Results showed that the superoxide dismutase (SOD) in hepatopancreas and muscle of P. sinensis significantly increased by ammonia nitrogen at 24h except muscle tissue in 220 mg/L, which decreased to the normal level at 48—96h. Compared with the control group, acid phosphatase (ACP) in hepatopancreas of P. sinensis by ammonia nitrogen treatment was not changed significantly at 24h, while alkaline phosphatase (AKP) was significantly increased. At 48—96h, both ACP and AKP were lower than the control group. Muscle ACP and AKP by ammonia nitrogen treatments except 140 mg/L were significantly lower than those in the control group at 24 and 96h. This study revealed that P. sinensis had strong tolerance to ammonia nitrogen. High ammonia nitrogen had can inhibit the activities of immune enzyme. The results will provide the scientific basis for the aquaculture of P. sinensis.