Abstract: Crustacean nitrogenous excretion was easily affected by environmental factors, such as ambient ammonia,salinity andpH. In order to investigate the effects of pH on ammonia excretion and heamolymph nitrogenous contents of Chinese mitten crab( Eriocheir sinensis),matured female crabs were exposed to pH 415,610,715,910 and 1015 for 24h,the ammonia excretion rateand haemolymph nitrogenous contents were determined after exposure. The results showed that there was no significant differenceof the ammonia excretion of E. sinensis frompH 415 to pH 910,but the inhibit effects on the ammonia excretion were observed atpH 1015 ( p < 0105). The haemolymph pH kept relatively constant at the levels of (7179 ±0102) - (7182 ±0101) frompH 415to pH 910, but increased significantly to 8. 2 ±0. 05 when exposed to pH 1015 ( p < 0105). The content of haemolymphammonia,urea and urate were also affect by environmental pH. The content of haemolymph ammonia increased from (4106 ±012)μg/ mL at pH 715 to (5190 ±0161)μg/ mL at pH 1015 and decreased to (1186 ±013)μg/ mL at pH 415. The haemolymph ureaand urate also affected by environmental pH,the content of urea and urate increased from (119 ±0112)μmol/ mL and (01139 ±6 6 水 生 生 物 学 报 32卷01003)μmol/ mL at pH 715 to (2147 ±0114)μmol/ mL and (01172 ±01012)μmol/ mL at pH 1015, respectively.At pH 415,theconcentrations of haemolymph were (1181 ±0108)μmol/ mL and (01096 ±01002)μmol/ mL,significantly lower than that of pH715. The high pH exposure also affected the metabolisms of protein and amino acids. The total haemolymph protein and haemo2cyanin concentrations exhibited unchanged from pH 415 to pH 910,but decreased significantly at the pH 1015. The content ofhaemolymph protein and haemocyanin were (76194 ±3108) mg/ mL and (0189 ±0101) mmol/ mL at pH 715, decreased to(57118 ±8149) mg/ mL and (0153 ±0103) mmol/ mL at pH 1015,respectively. In contrast, the total haemolymph free aminoacids increased significantly at pH 1015 ( p < 0105). The results indicated that exposure E. sinensis to high environmental pHcaused decrease in ammonia excretion rates,and elevated the contents of haemolymph ammonia,urea,urate and total free aminoacids,which might be contributed to the detoxification of ammonia.