To improve techniques of artificial breeding, this research focused on the novel membrane progestin receptor(mPRL) of half smooth tongue sole ünther. The full-length cDNA encoding mPRL wascloned from the half smooth tongue sole by means of homology cloning and RACE PCR analyses. The complete cDNAsequence of mPRL (GenBank accession number: KF277065) was 2 002 bp in length, consisting of a 5′′UTR of 783 bp. The molecular weight of mPRL was17.62 kD. Structural analysis of the translated cDNA suggested that it encoded membrane protein with seven transmembranedomains. Tertiary structure of the mPRL protein showed that it had several binding sites. The rooted phylogenetictree was constructed using the neighbor-joining method on MEGA4.0 for comparative analysis of half smoothtongue sole mPRL and selected vertebrate sequences. The similarity (%, identity) of half smooth tongue sole mPRL incomparison with other representative sequences was analyzed using Clustal X. The results indicated that the halfsmooth tongue sole mPRL was clustered with mPRL of other fish. Half smooth tongue sole had 68% identity withJapanese medaka (). The mPRL mRNAexpression in half smooth tongue sole was detected by quantitative real-time PCR. And found to be widely, althoughnot homogeneously expressed. mPRL transcripts were highly abundant in the brain, ovary, heart, gill, spleen, andstomach. In addition, positive signals were obtained for mPRL mRNA in the pituitary gland, muscle, and intestine, althoughthe resulting transcript levels were lower than in the ovary. Representative sections of ovaries showed the morphologicalcharacteristics during development, which was divided into five stages. The expression level of mPRLmRNA at various stages of oogenensis in the sole showed that the level of mPRL mRNA in the brain and ovary significantlyincreased from stage II to stage V (