The mRNA differential display technique was performed to investigate the differences in gene expression in the Longissimus dorsi muscle tissues from Landrace×Large White cross-combination. One novel gene that was differentially expressed was identified using semi-quantitative reverse transcriptasepolymerase chain reaction (RT-PCR) and its complete cDNA sequence was obtained using the rapid amplification of cDNA ends (RACE) method. The nucleotide sequence of the gene is not homologous to any of the known porcine genes. The sequence prediction analysis revealed that the open reading frame of this gene encodes a protein of 260 amino acids that contains the putative conserved domain of the carbonic anhydrase,and this protein has high homology with the carbonic anhydrase Ⅲ (CA-Ⅲ) of four species-mouse (91%),horse (91%), rat (89%) and human (86%)-so that it can be defined as swine carbonic anhydrase Ⅲ. The phylogenetic tree analysis revealed that the swine CA-Ⅲ has a closer genetic relationship with the horse CA-Ⅲ than with those of mouse, rat and human. The tissue expression analysis indicated that the swine CA-Ⅲ gene is generally expressed in most tissues. Our experiment is the first to establish the primary foundation for further research on the swine CA-Ⅲ gene.