Partial StAR gene sequence obtained from whole genome sequencing results of half-smooth tongue sole(Cynoglossus semilaevis)and its full-length cDNA sequence were acquired by SMART-RACE.The StAR complete cDNA was 1 294 bp in length containing 852 bp open reading frame(ORF)and encoded 283 amino acids,132 bp 5'un-translated region(5'-UTR)and 310 bp 3'un-translated region(3'-UTR).Alignment analysis of the amino acids sequence with other species showed that StAR of C.semilaevis was 85% similar to most species of StAR including Solea senegalensis,Micropterus salmoides,Lateolabrax japonicus and Sparus aurata.In order to study the relative expression of StAR gene between females and males,and in different stages of male,we chose the real-time fluorescence quantitative methods.The results indicated that StAR mRNA was extremely highly expressed in testis,but was hardly expressed in the ovary of C.semilaevis.From 16 days to 66 days,StAR gene was not expressed in testis.While 150 days the expression was significantly increased,until sexual maturity,StAR mRNA doubled the amount of expression.After the discharge of sperm,the expression declined obviously.This suggests that the gene has great function in the development of testis.To determine the temporal StAR expression,we chose the method of in situ hybridization.The result showed that StAR mRNA was expressed in sperm cells of testis.Our results showed that StAR gene played important roles in the testis maturation and displayed great function during the period of sperm formation.