The ridgetail white prawn Exopalaemon carinicauda is a euryhaline shrimp species in the estuarine and coastal areas of China. In this study, survival rates, transcription levels of two prophenoloxidase system-related genes (EcLGBP and EcproPO) and PO activity were determined quantitatively in juvenile and adult E. carinicauda under different salinity levels. The results showed that E. carinicauda juveniles could survive in a wider range of salinity conditions than adults. For juvenile E. carinicauda, the expression levels of EcLGBP and EcProPO were up-regulated in low salinities and showed no significant difference at 20-40, while PO activities in low salinities were higher compared to those in high salinities. For adult E. carinicauda, the expression profiles of EcLGBP and EcproPO had a different trend of up-regulation in salinity stress treatments and no obvious difference was observed in the gene expression levels and PO activity between 30 and 40. The salinity tolerance range of immunity for juvenile and adult E. carinicauda is 20-40 and 30-40, respectively.