Abstract: The ridgetail white prawn,Exopalaemon carinicauda supports a large yield of polyculture ponds in eastern China.However,the artificial breeding technique for E.carinicauda is not quite advanced,which limits the further development of the E.carinicauda culture,and there have been few studies on the mechanism of gonadal development and embryonic development.Recent studies have shown that ecdysteroid receptor(EcR)is not only involved in molting and growth of Arthropod but also plays important roles in ovarian development and embryogenesis.To study the regulatory role of EcR in ovarian development and embryogenesis of E.carinicauda,the full-length EcR cDNA of E.carinicauda(EcEcR)was cloned by the methods of degenerated oligonucleotide primers and rapid amplification of the cDNA ends(RACE),and quantitative real-time PCR was used to quantify the relative expression level of EcEcR in different tissues,ovarian development and embryogenesis of E.carinicauda.The results showed that the full-length EcEcR(GenBank accession number:KC506600)was 2 638 bp,containing an open reading frame(ORF)of 1 713 bp encoding a 570 amino acid polypeptide.Multi-sequence alignment analysis showed that EcEcR shared the high identities with Crangon crangon,Macrobrachium nipponens,Homarus americanus,however,it shared lower identity with EcRs from Marsupenaeus japonicas and Litopenaeus vannamei.EcEcR was expressed in various tissues and the highest in the heptopancreas.The EcEcR mRNA levels in ovary and heptopancreas of E.carinicauda reached a maximum at the stage Ⅲ and stage Ⅳ,respectively,and the EcEcR expression levels were higher in heptopancreas than in ovary during the ovarian development.However,the EcEcR mRNA levels in ovary at stages IV and V were significantly higher than those at stages Ⅰ and Ⅱ.Another very important finding was that significantly positive correlations existed between the EcEcR expression level and total vitellogenin content.During embryogenesis,the levels of EcEcR expression were higher at stages of gastula,protozoea and metazoea than those at other stages.The results indicated that the relationships displayed in the phylogenic tree of EcRs may correspond to their breeding practice,and EcEcR mRNA was expressed highly in hepatopancreas.EcEcR was involved in vitellogenin synthesis during ovarian development of E.carinicauda, and the EcEcR expression level in hepatopancreas was consistent with the gonadosomatic index.EcEcR played an important role in the ovarian maturation,and may play key roles in cell differentiation and organogenesis during embryo development.