Abstract: We cloned the MHC-Ⅰ gene from cobia (Rachycentron canadium) by homology cloning and RACE PCR. The full-length cDNA of MHC-Ⅰ comprises 1 330 bp with a 76 bp 5 untranslated region (UTR), a 189 bp 3 UTR and a 1 065 bp open reading frame (ORF), encoding a polypeptide of 354 amino acid residues with a predicted molecular weight of 40.10 kD and a theoretical isoelectric point of 5.70. According to the phylogenetic tree and amino acid similarity comparison, the homology of MHC-Ⅰ amino acids between cobia and some known fishes and human (Homo sapiens) varies from 27.9% to 67.1%. The putative protein sequence shows some important features including leader peptide, 1,2,3,CP/TM/CYT regions and conserved cysteines, etc.. Real-time PCR result indicates that MHC-Ⅰ expresses in all detected tissuesat different expression levels. High expression is detected in head kidney; moderate expression is detected in gill, spleen and intestine; while low expression is detected in heart, brain and muscle.