Abstract: As a key enzyme in the antioxidant systems of living organisms, catalase plays an important role in eliminating hydrogen peroxide against oxidative stress. The open reading frame (ORF) of catalase (GenBank Accession No. KKF14425.1) was cloned from large yellow croaker (Larimichthys crocea), which comprised 1584 bp, encoding a peptide of 527 amino acids (aa) in length, with a predicted molecular mass of 59.98 kDa and a theoretical isoelectric point of 8.37. Several highly conserved motifs, including the proximal active site signature " FDRERIPERVVHAKGA”, the proximal heme-ligand signature sequence " RLFSYPDTH”, the three catalytic amino acid residues of His⁷⁵, Asn¹⁴⁸ and Tyr³⁵⁸ and NADPH binding site were identified in the deduced amino acid sequence of CAT from large yellow croaker. Sequence comparison strongly suggested that this sequence was a member of CAT family and highly homologous with other known CAT of fish, especialy with Rachycentron canadum and Oplegnathus fasciatus (94%) of Sciaenidae, and they also gathered into the same branch in the phylogenetic tree. Constitutive CAT mRNA expression was detected in seven tissues of large yellow croaker with different magnitudes, which was high in liver and low in muscle, suggesting its diverse role in physiology with respect to the tissue type. The mRNA of HSP70 in liver after infection by Vibrio anguillarum was detected based on RT-PCR analysis. The transcriptions of CAT were upregulated, the maximum level appeared at 12 h post-injection with 7.48-fold and dropped back to the original level at 72 h post-injection, which showed a slight rise in the group of PBS injection. The results indicated that CAT in L. crocea can function as a potent antioxidant enzyme in large yellow croaker and may play a role in postimmune responses with respect to its peroxidase activity.