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 of CAT 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 (P < 0.05), and then recovered to normal at 24^th hour and 48^th 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 12^th hour (P < 0.05);under the stress of pH 9.0, the expression of PmCAT declined (P < 0.05). The results reveal that PmCAT plays a significant role in adaptive response to conditions of oxidative stress and environmental toxicity.