Retinoid X receptor(RXR)is a member of the second subfamily of nuclear receptor superfamily.In the insect and the crustacean,RXR is an important signaling protein with varied roles in regulating aspects of reproductive maturation,molting and embryo development.In this study,we cloned RXR gene from Eriocheir sinensis using reverse transcriptase polymerase chain reaction(RT-PCR)and rapid-amplification of cDNA ends(RACE),and primers were designed according to the conserved sequence of RXR from Gecarcinus lateralis.The full-length cDNA sequence of RXR is 1 517 bp and codes a protein of about 433 amino acids.The amino acid sequence comparison results showed that the RXR gene of Eriocheir sinensis shared 96% identity with Gecarcinus lateralis,using BLASTn and BLASTx software.Phylogenetic tree of RXR gene generated by Neighbor Joining method suggested that RXR is clustered closely with that of Gecarcinus lateralis.The expression of the gene in different tissues and molting stages of E.sinensis was analyzed by real-time fluorescent quantitative PCR.The result showed the RXR mRNA was expressed in all tissues examined and highly in Y-organ,with small amount in hepatopancreas,gill and muscle,trace in heart,stomach,intestine,thoracic ganglion and brain ganglion.RXR mRNA was detected with high volume in Y-organ compared to hepatopancreas,muscles and gill at the same molting stages of the crab.RXR mRNA of Y-organ in stage D was significantly(P<0.05)higher than that of stage AB and stage C.It also had significant difference(P<0.05)between muscles at stage AB and stage E,and there was no significant difference expression in hepatopancreas and gill tissues in different molting stages.