Abstract: Catalase (CAT) is an antioxidant enzyme and plays an important role in protection against oxidative stress by scavenging hydrogen peroxide (H2O2). We obtained the full-length cDNA sequence ofCAT from black tiger shrimps ( Penaeus monodon) ( denoted as PmCAT) by transcriptome sequencing and RACE-PCR. The full-length cDNA of PmCAT was 1 909 bp，including an open reading frame ( ORF) of 1 563 bp encoding a polypeptide of 520 amino acids，a 5'UTR of 134 bp and a 3'UTR of 212 bp. Blast and phylogenetic analyses suggest that PmCAT is a CAT family member. The expression of PmCAT mRNA showed a declining trend under the stress of CuSO4 (P0.05), and then recovered to normal at member 24th hour and 48th hour, being the highest in gill, and then in hepatopancreas and thoracic nerves. Under the stress of pH 7.0，PmCAT expression reached the maximum at 12th hour (P0.05); under the stress of pH 9.0, the expression of PmCAT declined (P0.05). The results reveal that PmCAT plays a significant role in adaptive response to conditions of oxidative stress and environmental toxicity.