Full-length cDNA encoding membrane progestin receptor alpha gene (mPRα) was firstly cloned from half smooth tongue sole Cynoglossus semilaevis Günther by homology cloning and RACE-PCR analysis. The length of complete cDNA sequence of mPRα gene was 1 319 bp. Sequence alignment of deduced amino acid of tongue sole mPRα and amino acid of other species showed that there were seven transmembrane domains. The rooted phylogenetic tree was constructed by the neighbor-joining method of MEGA 4.0, and the identity of tongue sole mPRα with other representative sequences was analyzed by ClustalX. The results indicated that the tongue sole mPRα was clustered together with mPRα of other fish. The identity was 94%, 93% and 90% when compared with Southern flounder Paralichthys lethostigma, Atlantic croaker Micropogonias undulates and Japanese medaka Oryzias latipes, respectively. In contrast, identity among the mPRα of tongue sole and that of human Homo sapiens and cattle Bos taurus was low, only 53%. A semi-quantitative RT-PCR was developed to measure mRNA expression levels of mPRα gene of female tongue sole. Tissue expression analysis showed that mPRα mRNA was expressed widely in tongue sole, although the expression level was not homogeneous. mPRα transcripts were highly abundant in brain, kidney, spleen and ovary, less abundant in liver, stomach and muscle.