To study the regulatory role of ecdysteroid receptor(EcR)in molting and ovarian development of crustaceans,the full-length EcR cDNA of Portunus trituberculatus(PtEcR)was cloned by using reverse transcript PCR(RT-PCR)and rapid amplification of cDNA ends(RACE).The full-length of PtEcR(GenBank accession number:KC354381)was 2 231 bp,included a 1 269 bp ORF which encoded 422 amino acid residues.The alignment of amino acid sequence of PtEcR and that of other crustaceans showed that their identities were 67% to 97%.Phylogenetic analysis of EcR showed PtEcR was clustered in crustaceans EcRs and separated from insect EcRs.Quantitative real-time PCR(qRT-PCR)was used to quantify the relative expression level of PtEcR in different tissues,molting process and the second ovarian development in P.trituberculatus .PtEcR was expressed in various tissues and highest in the Y-organ(YO).During the molting process,the expression levels of PtEcR in YO remained low from postmolt period to substages of D2 premolt period,then significantly increased at substages D3 and D4.The changes in the expression levels of PtEcR were consistent with those in the levels of hemolymphatic 20-hydroxyecdysone,which demonstrated that PtEcR played an important role in molting regulation of P.trituberculatus.During the second ovarian development,the expression levels of PtEcR in YO and hepatopancreas gradually increased to the maximum from stage Ⅱ to Ⅳ;The expression levels of PtEcR in ovary at stages Ⅱ and Ⅳ were significantly higher than those at stage Ⅰ and Ⅲ.The results indicated that PtEcR may play an important role during ovarian development in P.trituberculatus.