Objective To investigate whether CD146, a cell adhesion molecule, is expressed in mouse and human preimplantation blastocysts and to localize CD146 in the layer of trophectoderm(TE) and/or inner cell mass(ICM). Methods Human and mouse embryos were collected. Using reverse transcription-polymerase chain reaction(RT-PCR), the expression of CD146 mRNA in blastocyst was evaluated in human and mouse embryos. Single embryo immunohistochemical staining was applicated in the examination of the expression of CD146 in protein level. The statistical significance of the data was analyzed using t-test. Results CD146 transcript was detected in all human and mouse preimplantation morula and blastocyst. The expression of CD146 was found to localize in human and mouse compacted morula stage embryos and the TE and ICM of the expanded blastocysts. Conclusion mRNA and protein of CD146 was expressed in preimplantation embryos, which may have a profound influence on early preimplantation development for the differentiation of the trophectoderm and the morphogenesis of the blastocyst. Furthermore, the expression of CD146 in blastocyst stage may be implicated in the assistance of embryo implantation. Objective To investigate whether CD146, a cell adhesion molecule, is expressed in mouse and human preimplantation blastocysts and to localize CD146 in the layer of trophectoderm (TE) and / or inner cell mass (ICM). Methods Human and mouse embryos were collected. reverse transcription-polymerase chain reaction (RT-PCR), the expression of CD146 mRNA in blastocyst was evaluated in human and mouse embryos. Single embryo immunohistochemical staining was applicated in the examination of the expression of CD146 in protein level. The statistical significance of the The results of CD146 was found to localize in human and mouse compacted morula stage embryos and the TE and ICM of the expanded blastocyst. Conclusion CD146 transcript was detected in all human and mouse preimplantation morula and blastocyst. mRNA and protein of CD146 was expressed in preimplantation embryos, which may have a profound influence on early preimplantation development for the differentiation of the trophectoderm and the morphogenesis of the blastocyst. The expression of CD146 in blastocyst stage may be implicated in the assistance of embryo implantation.