Abstract: In order to study the influence of pH on the respiratory and excretion of U. unicinctus, the impacts of different pH (5、6、7、8、9) on the oxygen consumption rate (OR), ammonia excretion rate (AR), energy metabolism rate (M) and O/N ofU. unicinctuswith body weights of 5.65±1.06g were observed. The results indicated that pH had a significant effect on OR, AR, M and O/N (p<0.05). The OR of U. unicinctus increased with increasing pH. It reached peak at pH 8 and then decreased with increasing pH. The quadratic polynomial model between the OR ofU. unicinctusand the pH is expressed as the following: OR=-2.977X² +55.188X-176.380，R² =0.937. The change of AR was similar to OR. The AR reached the maximum at pH 7 and the minimum at pH 9. The differences between pH 8 and pH 9 groups were not significant (p>0.05). The relationship of the AR with pH could be expressed as the following: NR=-0.350X² +4.442X-6.822，R² =0.724. The M and O/N ofU. unicinctus increased firstly with increasing pH and then decreased resulted in the polynomial modelsM=-0.040X² +0.424X-0.044，R² =0.937; A =0.053X² +1.879X-7.470，R²=0.901. At pH 8 the level of protein metabolism was the lowest, which was beneficial to the accumulation of protein. The results showed thatU. unicinctus could adjust physiological metabolic level to adapt to the pH of water in a certain pH range and weak alkaline water was suitable for U. unicinctus to live and the optimum pH was 8.