Major histocompatibility complex (MHC) plays an important role in the immune response of vertebrates. Its function is to present self and non-self peptide to T-cells receptor. In order to study the function and molecular polymorphism of class II genes in teleost, MHC IIB was identified from by expressed sequence tags (ESTs) and rapid amplification of cDNA ends (RACE) approach. was of 1 144 bp, consisting of 5’ UTR of 7 bp, a 3’ UTR of 450 bp with a poly (A) tail, and an open reading frame (ORF) of 687 bp encoding a polypeptide of 228 amino acids, which contained a signal peptide, a peptide-binding region (β1), an immunoglobulin-like region (β2), a transmembrane region and a cytoplasmic region. Phylogenetic analysis demonstrated that the putative MHC IIB amino sequence showed 30%-79% identity with those of other teleosts and and other known class IIB genes was that β2 domain-encoding exon was split by an intron of 109 bp in length. There were 23 single nucleotide variable sites in exon 2. Realtime PCR analysis demonstrated that was ubiquitously expressed in nine tested tissues, but the expression levels were different. The expression levels in kidney, heart, spleen and gill were significantly higher than those in liver, skin, brain, blood and muscle.