Post-ovulatory oocyte aging degrades the quality and developmental competence of embryos for implantation. To evaluate the effects of oocyte aging on the initial differentiation of embryos, we examined trophectoderm (TE) formation and the expressions of TE differentiation-related signaling molecules in embryos derived from in vitro aged oocytes. Murine ovulated oocytes were incubated for 6 h or 12 h in vitro after collection (aged oocytes). Oocytes examined immediately after collection were used as controls. All oocytes were subjected to intracytoplasmic sperm injection (ICSI), and some of the developed embryos were examined for their expressions of phosphorylated FGFR2 (p-FGFR2), p-MEK, p-ERK, and CDX2 by immunofluorescence staining or immunoblotting. The remaining embryos were transferred to the uteri of pseudopregnant foster mothers. Embryos derived from aged oocytes had poor competence during early development and fewer TE cells at the blastocyst stage. In these embryos, the expression of CDX2 which is involved in TE differentiation and FGFR2/Mitogen-activated protein kinase (MAPK) signaling which regulates CDX2 expression were attenuated. This may have reduced their implantation and post-implantation competence. These findings suggest that post-ovulatory oocyte aging weakens the expression of TE differentiation-related factors and affects initial differentiation into TE and extra-embryonic tissue lineages in embryos after fertilization.