The full length DNA and cDNA of IgZ gene from swordtail fish Xiphophorus hellri were cloned.The obtained DNA of IgZ is 5 420 bp in length, which is composed of four exons and three introns.The length of cDNA is 1 527 bp, containing a 1 299 bp open reading frame(ORF)which encoded a protein of 432 amino acids with deduced protein molecular weight 47.48 ku.Alignment based on amino acid sequence indicates that swordtail fish IgZ shared similarities of 28%-54% with other fishes.IgZ mRNA expression of swordtail fish was predominantly detected in head kidney, spleen and intestines.The expression levels of IgZ in the head kidney and spleen both demonstrated peaks at 4 days post immunization, increasing of approximately 2 fold and 4 fold in comparison with control group, respectively.Moreover, the expression level of IgZ in intestines varied more sensitively with increasing about 11 fold in comparison with control in the second day after immunization.The results further reveal the IgZ gene plays an important role in the intestinal mucosal immunity.Furthermore, this study also indicates that the swordtail fish could be utilized as a useful fish model for the research of fish diseases and vaccine evaluation.