Abstract: It was approached that the immune response of soft-shelled turtle , Trionyx sinensis , was influenced by its age , size and nutrition .The response of 2 years old turtle against bacteria T3was enhanced with the size increasing , especially when the weight was below 40g .In contrast , this phenomenon was not found in 1 year old turtle and its response was fluctuated on a lower or medium level .At the same weight the immune response of 2 years old turtle against T3 was much stronger than that of 1 year turtle .However , the response was weakened at a certain degree in the undernourishment .