In order to find more functional genes with EF-hand domain in Hyriopsis cumingii,we cloned the full-length cDNA of EF-hand calcium-binding domain-containing protein 1(EFCB1)by using RACE-PCR technique,and performed bioinformatics analysis;EFCB1 gene expression levels were analyzed in different tissues from Hyriopsis cumingii(mantle pallial,gill,visceral mass,adductor muscle,axe foot,gonad,liver,gut,haemolymph and kidney)and in different periods of the mantle and visceral mass after inserting nucleus.The results showed that the EFCB1 cDNA sequence length was 981 bp,containing a 531 bp open reading frame(ORF)encoding 176 amino acid residues,239 bp 5'-untranslated region(UTR)and 211 bp 3'-UTR.The molecular weight of the peptide was predicted 19.9 ku,with an isoelectric point of 4.70.Amino acid sequence analysis showed that there was a transmembrane region.Results of the ProtScale online analysis showed that the protein was hydrophilic protein.There were two typical EF-hand calcium binding domains,respectively DLNDDKLISPEE(98-109)and DTNGDDKLDGEE(129-140).Phylogenetic analysis indicated that the EFCB1 of H.cumingii was closely related to seawater bivalve Crassostrea gigas,followed by that of fish and then insect.Real-time Q-PCR results showed that the EFCB1 mRNA is ubiquitously expressed in various tissues(mantle paillial,gill,visceral mass,adductor muscle,axe foot,gonad,liver and gut),with the highest level in the gut and gill(P<0.05),and it is also highly expressed in the pearl culture tissues(mantle and visceral mass).These data suggested that EFCB1 plays an important role in the absorption process of Ca²⁺,and there might be an intrinsical relationship between EFCB1 and pearl formation of H.cumingii.Furthemore,expression differences were found among different periods of the mantle and visceral mass after inserting nucleus in the H.cumingii,and the expression level of EFCB1 in the mantle was significantly higher than that in visceral mass(P<0.05),after nucleus inserted 20 d it was significantly higher than other periods(P<0.05),suggesting EFCB1 has an important function in the formation process of pearl sac and nacre secretion,indicating EFCB1 might be an important regulator of pearl formation.The results of present study may provide useful information for further studies on regulation mechanism of calcium metabolism and pearl formation.