Abstract: To investigate the toxic effects of ammonia on the early life history stages of mussels, we selected glochidia and newly transformed juveniles of Cristaria plicata, a common mussel species in the middle and lower reaches of the Yangtze River, and conducted 24h and 48h acute toxicity tests to assess the effects. The results showed that: the 24h lethal concentration of 50% (LC50) of ammonia in glochidia of Cristaria plicata was 0.63 mg NH₃-N/L (NH₃-N, unionized–ammonia nitrogen) or 78 mg TAN_{7.0, 20℃}/L (TAN, standardized total ammonia nitrogen that pH 7.0 and water temperature of 20℃). The 48h LC50 of ammonia in newly transformed juveniles of Cristaria plicata was 0.60 mg NH₃-N/L or 104 mg TAN_{7.0, 20℃}/L. The LC50 of ammonia to Cristaria plicata was higher compared to other freshwater mussels species reported both domestically and internationally. The early life stages of Cristaria plicata were more sensitive to ammonia compared to the later life history stages. The results of this study contribute to a better understanding of ammonia toxicity on mussels and provide a scientific basis for mussels conservation and water nitrogen management strategy.