Cysteine-cysteine chemokine receptor 9 (CCR9) homologue cDNA was isolated from olive flounder leukocyte cDNA library. Olive flounder CCR9 homologue consisted of 1709 bp encoding 367amino acid residues. When compared with other known CCR peptide sequences, the most conserved region of the olive flounder CCR9 peptide is the seven transmembranes. A phylogenetic analysis based on the deduced amino acid sequence showed the homologous relationship between the olive flounder CCR9 sequence and that of Mouse CCR9. The olive flounder CCR9 gene was predominantly expressed in the Peripheral blood leukocytes (PBLs), kidney, spleen, and gills.