Abstract: The objective is to study the toxic effects of ammonia and nitrite on Xiphophorus hellerii and Poecilia reticulate, and determine the safe concentration of ammonia and nitrite to Xiphophorus hellerii and Poecilia reticulate with the test method for the acute toxicity of static water. The chronic toxicity test was conducted to determine the effects of ammonia and nitrite on antioxidant indices. The results showed that there was no difference in the 24, 48, 72, 96 h lethal concentration of ammonia nitrogen and non- ionic ammonia for Xiphophorus hellerii and Poecilia reticulate (P>0.05). However, the 24, 48, 72, 96 h lethal concentration and safe concentration of nitrite for Xiphophorus hellerii were significantly lower than those of Poecilia reticulate (P< 0.05). The safe concentration of ammonia, non-ionic ammonia, and nitrite of Xiphophorus hellerii was 12.22, 0.59 and 0.52 mg/L, respectively. The safe concentration of ammonia, non- ionic ammonia and nitrite for Poecilia reticulate was 12.54, 0.55 and 1.77 mg/L, respectively. No difference was observed in gill Na+/K+- ATPase, SOD activity and T-AOC after exposed to ammonia and nitrite at the safe concentration for 96 h (P> 0.05). However, gill Na +/K +- ATPase activity decreased after exposed to ammonia and nitrite at the concentration of 0.5×LC50,96h (P<0.05). Therefore, the concentration of amino and nitrite should be controlled below the safe concentration in rearing Xiphophorus hellerii and Poecilia reticulate.