Catalase(CAT) and selenium-dependent glutathione peroxidase(Se-GPx) play a vital role in protecting organisms against various oxidative stresses by eliminating H2O2. The objective of this paper is to evaluate the roles of these antioxidant molecules in the ridgetail white prawn Exopalaemon carinicauda in response to low salinity stress. A complementary DNA(cDNA) containing the complete coding sequence of CAT was cloned from the hepatopancreas using reverse-transcription polymerase chain reaction(RT-PCR) and rapid amplification of cDNA ends. The full-length cDNA of CAT(2 649 bp) contains a 5’-untranslated region(UTR) of 78 bp, a 3’- UTR of1 017 bp, with a poly(A) tail, and an open reading frame of 1 554 bp encoding a 517-amino-acid polypeptide with predicted molecular mass of 58.46 kDa and estimated isoelectric point of 6.64. This CAT sequence contained the proximal active site signature(60FDRERIPERVVHAKGAG76), proximal heme-ligand signature sequence(350RLFSYPDTH358) and three catalytic amino acid residues(His71, Asn144 and Tyr354). Sequence comparison showed that the CAT deduced amino acid sequence of E. carinicauda shared 68%-92% of identities with those of other species. Quantitative real-time PCR analysis revealed that CAT m RNA was widely expressed in the hepatopancreas(highest), hemocyte, eyestalk, heart, gill, muscle, ovary and stomach. Under low salinity stress,CAT and GPx m RNA expression levels both in the gill and hepatopancreas increased significantly at the first 48 h and 6 h respectively, indicating a tissue- and time-dependent antioxidant response in E. carinicauda. All these results indicate that E. carinicauda CAT is a member of the CAT family and might be involved in the acute response against low salinity stress. Catalase (CAT) and selenium-dependent glutathione peroxidase (Se-GPx) play a vital role in protecting organisms against various oxidative stresses by H2O2. The objective of this paper is to evaluate the roles of these antioxidant molecules in the ridgetail white prawn Exopalaemon carinicauda in response to low salinity stress. A complementary DNA (cDNA) containing the complete coding sequence of CAT was cloned from the hepatopancreas using reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends. The full- length cDNA of CAT (2 649 bp) contains a 5’-untranslated region (UTR) of 78 bp, a 3’-UTR of 1 017 bp, with a poly (A) tail, and an open reading frame of 1 554 bp encoding a 517 -amino-acid polypeptide with predicted molecular mass of 58.46 kDa and estimated isoelectric point of 6.64. This CAT sequence contained the proximal active site signature (60FDRERIPERVVHAKGAG76), proximal heme-ligand signature sequence (350RLFSYPDTH358) and three catalytic amino acid residues (His71, Asn144 and Tyr354). Sequence comparison showed that the CAT deduced amino acid sequence of E. carinicauda shared 68-92% of identities with those of other species. Quantitative real-time PCR analysis revealed that CAT m RNA was widely expressed in the hepatopancreas (highest), hemocyte, eyestalk, heart, gill, muscle, ovary and stomach. Under low salinity stress, CAT and GPx m RNA expression levels both in the gill and hepatopancreas increased significantly at the first 48 h and 6 h respectively, indicating a tissue- and time-dependent antioxidant response in E. carinicauda. All these results indicate that E. carinicauda CAT is a member of the CAT family and might be involved in the acute response against low salinity stress.