PRLI is an important osmoregulation hormone, which belongs to GH/PRL/SL hormone family. Its most important role in tilapia is to change the osmotic pressure of plasma through changing the activity of Na⁺-K⁺-ATPase. Through crossbreeding we got a new hybrid between . The hybrid grows faster than the male parent and shows a stronger osmoregulation ability than the female parent. In order to explore the molecular mechanism of salinity tolerance of tilapia, learn and screen the related genes about salinity tolerance, through RT-PCR we cloned and analyzed the cDNAs encoding prolactin from characterized by fast growth but low salinity tolerancecharacterized by high salinity tolerance but slow growth and from their hybrid characterized by ideal growth and salinity tolerance. First（Escherichia coli and sequenced. And the PRLI nucleotide and amino acid sequence were analyzed. Major results are as followsThe sequence cloning and Clustal X1.83 analysis showed that PRL of three genotypes of tilapia consists of 339 bp and encodes a putative protein of 112 amino acids.There was 97.94%-99.71% identity in nucleotide sequenceover 99.11% identity in amino acid sequence among three genotypes of tilapia, indicating high conservation of PRLI gene in tilapias.O. niloticusthere were five varieties in nucleotide with 1.47% in proportion; In hybrid vswith 0.3% in proportion.On the amino acid sequence the 80th point in was proline residuebut in S. melanotheron and hybrid it was serine residuePhylogenetic tree of MEGA4 showed that the hybrid and S. melanotheron were clustered into one group. Resultsjointly indicate that the hybrid is closer to its paternal line.