Lex[Galβ1–4(Fucα1–3)GlcNAc] and Ley[Fucα1–2Galβ1–4(Fucα1–3)GlcNAc] are both stage‐specific embryonic antigens. Lex is first detected on the blastomeres of the 8‐cell stage embryo, which correlates with the onset of blastomere compaction. Ley is highly expressed on the surface of the blastocyst, which has been shown to be involved in blastocyst attachment in the mouse. In the present study, mouse α1,2‐FT (also known as FUT1) and α1,3‐FT (also known as Fuc‐TIV), which were responsible for Lex and Ley formation, were examined in preimplantation stage embryos by reverse transcription‐PCR and in situ hybridization. α1,3‐FT mRNA was detected in all embryos of preimplantation stage, while α1,2‐FT mRNA emerged in the later stage embryos from 8‐cell to 16‐cell to the blastocyst. These results indicated the expression of Ley was regulated by α1,2‐FT. In situ hybridization showed that these two enzyme mRNAs were detected only in morula and blastocyst stage embryos. The α1,2‐FT and α1,3‐FT mRNAs were located in both the inner cell mass and the trophoblast cells. 2‐Cell and 4‐cell embryos were isolated from the oviduct and cultured in vitro to the 8‐cell, morula and blastocyst stage. The expression of α1,2‐FT and α1,3‐FT were observed in these embryos developed in vitro; immunohistochemical analysis also showed that Ley expression was positive. These results suggested the stage‐specific expression of Ley on the embryos was synthesized by endogenous α1,2‐FT and α1,3‐FT rather than transfer from other sources. In addition, the expression of α1,2‐FT was differentially regulated and the uterine factor was not prerequisite of the expression of Ley.