Abstract: To investigate the impact of ammonia nitrogen stress on the acute toxicity and antioxidant responses of Misgurnus anguillicaudatus and Paracheilus dabryanus, a static toxicity test was conducted on M. anguillicaudatus body weight (8.13 ± 1.04) g and P. dabryanus body weight (8.72 ± 1.33) g. The semi-lethal concentrations of ammonia nitrogen over 72 hours were determined as 610.45 mg/L and 516.90 mg/L for M. anguillicaudatus and P. dabryanus, respectively. Correspondingly, the non-ionic ammonia concentrations were found to be 5.04 mg/L and 4.26 mg/L. Upon exposure to a semi-lethal mass concentration of 100 mg/L ammonia nitrogen, the impact on the antioxidant function of the liver and muscles in both mud fish species was examined. The results indicated that following ammonia nitrogen stress, the levels of malondialdehyde (MDA), superoxide dismutase (SOD), lysozyme (LZM), and glutathione peroxidase (GPx) activities all exhibited varying degrees of increase. Notably, the antioxidant enzyme activity of M. anguillicaudatus surpassed that of P. dabryanus. These findings suggest that M. anguillicaudatus displays a more robust antioxidant response compared to P. dabryanus under ammonia nitrogen stress conditions.