Abstract: Major Histocompatibility Complex class I (MHC class I) proteins are critical for immune defenses against viruses. Polygeny and polymorphism of alleles contribute to the breadth of the immune response. In previous study, researchers showed that a MHC class I gene termed Ctid-AB190929 was found from a grass carp. It was a expressed gene from cDNA library. Now, characterization of a genomic clone from the same grass carp constructed fosmid genome library allows us to further analysis the MHC class I region. This clone carried whole MHC class I and tapasin gene. This MHC class I termed Ctid-UBA0201 was the classical MHC class I by genomic analysis. But the amino acid sequences of Ctid-UBA0201 were differed from that of Ctid-AB190929. As lower vertebrates, appear to use a single expressed MHC class I locus to present a wide variety of peptide to antigen. The Ctid-UBA0201 could be the allelic gene of Ctid-AB190929. As the tapasin gene may be a unexpressed gene by genomic analysis, the Ctid-UBA0201 may present a wide variety of peptide without the tapasin gene to control the assembly. It may preserve genetic diversity which can be exchanged when the species face a new pathogen.