Molluscan engrailed proteins and bone morphogenetic proteins have attracted lots of interests in their potential important roles during embryonic shell compartment boundary formation. Engrailed is also proposed to be one of the important regulators of matrix proteins regional expressions in oyster mantle tissue, therefore determination of the regulation mechanisms on the particular expression patterns of engrailed in mollusks would be of great scientific value. However the study has been bogged down because the whole genomes of the oysters have not been sequenced completely and no oyster cell lines are available at present so that many genes of the regulators and mediators need to be cloned and classic signal pathways assays are hard to be applied. In previous study, the bone morphogenetic protein 2 (BMP2) and the oyster mothers against decapentaplegic 3 homolog (Smad3) have been identified from the pearl oyster Pinctada fucata. It is interesting to investigate the relationships among the oyster engrailed, BMP2 and Smad3 expressions in the oyster. Thereby a partial fragment of an engrailed homolog has been amplified from the genome template of the pearl oyster Pinctada fucata. Alignments with the deduced amino acids sequence show that the DNA-binding homeobox (EH4) domain of the oyster engrailed shares extremely high similarities with other engrailed proteins. Shell notching experiment and semi quantitative polymerase chain reaction results suggest that the change pattern of the oyster engrailed mRNA level is similar to that of the oyster mothers against decapentaplegic 3 homolog (Smad3) in shell repair process. Then the Smad3, the engrailed and the BMP2 mRNA expression levels in primary cultured oyster mantle tissue cells that are treated with dexamethasone (DXM) and hydrogen peroxide (H₂O₂) respectively have been examined. Real time quantitative polymerase chain reaction results show that the engrailed, the Smad3 and the BMP2 mRNA levels in the oyster mantle cells exhibit significant correlations with each other. All the results provide important clues and basis for further study on developmental and signal transduction mechanisms on oyster biomineralisation.