Ecdysteroid receptor(EcR)could mediate the regulation effect of ecdysteroid hormone(EH),and plays important roles in molting and growth of Arthropod.To study the structure and function of ecdysteroid receptor(EcR)gene in Eriocheir sinensis,a complete cDNA sequence encoding EcR(Ers-EcR,GenBank Accession No:KF736985)was cloned from Y-organ of E.sinensis by 5' and 3' RACEs.The full-length cDNA consists of 2 176 bp with a 1 638 bp open reading frame,encoding 545 amino acids without signal peptide.Typical domains of nuclear receptor super family:DNA binding domain(DBD)and ligand binding domain(LBD)were identified by SMART(simple modular architecture research tool)in Ers-EcR.DNA binding domain contains 8 conserved cysteines forming two zinc finger motifs(C¹⁵⁶-C¹⁵⁹-C¹⁷³-C¹⁷⁶,C¹⁹²-C¹⁹⁸-C²⁰⁸-C²¹¹),which is the typical character of DNA binding domain.Multi-sequence alignments analysis showed Ers-EcR shared the highest identity with Uca pugilator(91%),also shared high identities with Callinectes sapidus(88%),Scylla paramamosain(87%)and Portunus trituberculatus(83%),however,it showed lower identity with EcRs from shrimps and insects.Phylogenetic analysis revealed that Ers-EcR was closely related to U.pugilator and Gecarcinus lateralis.Tissue distribution of Ers-EcR was detected by quantitative real-time PCR,although strong expression of Ers-EcR was detected in muscles and Y-organ,and its expression could also be found in eyestalk,intestine,hepatopancreas,heart,haemocyte,ovary,testis,thoracic nerve cord and gill.This study would facilitate the study of the roles of Ers-EcR in molt and growth regulation in crustacean.