Abstract:To reveal the gene sequences of prolactin and its expression in osmotic regulation tissue of Cyprinus carpio var.Jian, the full length cDNA encoding prolactin was cloned from Cyprinus carpio var.Jian using homology cloning and RACE PCR approach. The prolactin was 1 028 bp in length, including 51 bp 5’terminal UTR, 633 bp encoding region and 344 bp 3’terminal UTR. Phylogenetic analysis using MEGA 4 software showed that the putative prolactin amino acid sequence and other teleosts have the high similarity of 55.02%-94.76%. The prolactin amino acid sequence of Cyprinus carpio var.Jian and that of Ctenopharyngodon idella were close to each other in similarity of 94.76%. For other fishes, the similarity was 94.26%,90.00%,70.53%,70.53%,65.70%,63.90%,63.29%,62.93%,62.38%,62.32%,55.02% with Schizothorax prenanti, Danio rerio, Salmo salar, Oncorhynchus mykiss, Anguilla japonica, Oreochromis Niloticus, Epinephelus coioides, Acanthopagrus schlegelii, Paralichthys olivaceus, Sparus aurata, Takifugu rubripes, respectively. Real time quantitative PCR results indicated that prolactin genes were expressed in the pituitary, brain, liver, kidney, intestines, gonad, spleen and gills. The prolactin transcript was detected at a high level in pituitary, moderate in brain, gills, spleen, liver, kidney and intestines, and low in gonad. This suggests that the pituitary gland is the main expression site of prolactin in Cyprinus carpio var.Jian.The prolactin transcript was detected in the gonads, liver, and spleen suggests that there may exist many physiological functions about prolactin in fish.