Abstract: The prostaglandin E4 receptor（EP4） is one of the prostaglandin E2（PGE2） receptor subtypes, and is a kind of G protein coupled receptor（GPCR）, which can participate in the regulation of cell physiological activities by regulating the concentration of cyclic adenosine monophosphate（cAMP）. In order to explore the functional differentiation and expression regulation mechanism of EP4 of Pinctada fucata martensii, we obtained the full cDNA sequence of two EP4 genes of P. f. martensii（PmEP4-1 and PmEP4-2） by using RACE technology, and used Real-time quantitative PCR（qPCR） to detect their expression difference in various tissues and analyzed their functional differentiation in different tissues. And then, we used bioinformatics methods to analyze their expression regulation mechanism and explore their functional differentiation mechanism. The results showed that the full-length cDNA of PmEP4-1 was 1 575 bp, including 1 098 bp of open reading frame（ORF）that encoded 365 amino acids. While PmEP4-2 gene was 1 976 bp, including 1 533 bp of the ORF which encoded 510 amino acids. Sequence analysis shows that the amino acid sequence of PmEP4-1 and PmEP4-2 in the intracellular and extracellular parts are quite different, and the number of protein functional sites is also different, indicating that there may be differences in their functions. Phylogenetic tree analysis showed that PmEP4-1 and PmEP4-2 originated from different ancestral genes. qPCR results showed that both of PmEP4-1 and PmEP4-2 were expressed in all tissues, but showed different expression modes, PmEP4-1 had the highest expression in blood, while PmEP4-2 has the highest expression level in the hemolymph. Bioinformatics analysis shows that the expression of PmEP4-1 is regulated by transcription factors such as Mat1-Mc, XFD-2, and Oct-1, while the expression of PmEP4-2 is regulated by transcription factors such as Oct-1, CF2-II, and Barbie Box. This research provided the basis for the further study of EP4 in P. f. martensii.