Abstract: To evaluate the effects of ammonia stress on growth, immunity, and histological structure of juvenile Taiwan loach (Paramisgurnus dabryanus ssp. Taiwan), the mean body mass of (2.00±0.56) g were exposed to different ammonia-N levels of 0 (control), 3.5, 6.0, 10.4 and 18.0 mg/L for 56 days. The results showed that the final weight (FW), weight gain rate (WGR), and specific growth rate (SGR) decreased significantly with the increased ammonia concentration, but there were no significant difference in survival rate among the groups. The activities of superoxide dismutase (SOD), alkaline phosphatase (ALP) in liver, and Na⁺K⁺ -ATPase in gill in the 10.4 mg/L and 18.0 mg/L groups were significantly lower than those of the control group. The activity of lysozyme (LZM) in the 18.0 mg/L group was significantly lower than that of the control group (P<0.05), and the content of malondialdehyde (MDA) was significantly higher than that of the control group (P<0.05). Epithelial oedema, epithelial necrosis and desquamation, cellular vacuolation and shortening of secondary lamellae were observed in gill after ammonia-N exposure. Meanwhile, karyolysis, cellular peripheral nucleus, hydropic degeneration, dilatation in sinusoids, cellular outline indistinguishable and cytolysis were observed in liver. Furthermore, the size of histological lesion area was positively correlated with the concentration of ammonia. These results indicated that ammonia-N stress inhibited the growth of juvenile Taiwan loach, disturbed the activities of immunity related enzymes were disturbed, and damaged the histological structure of gill and liver.