Preimplantation development refers to the early embryonic development between fertilization and implantation. During this short developmental window (4.5 days of mouse), a series of morphological and developmental changes take place. In morphology, three important changes occurred during preimplantation development in mouse embryos: compaction and polarity at 8-cell stage; inner cell mass and trophectoderm differentiation at early blastocyst stage; epiblast and primitive endoderm segregation at late blastocyst stage. In developmental biology, chromatin reprogramming, degradation of maternal factor, and embryo genomic activation take place after fertilization. Taken preimplantation embryos of mouse as an example, the present review aims to highlight the regulatory mechanisms responsible for the change of embryo morphology, and related signaling pathways of early embryonic cell differentiation, which are essential for the lineage specification. Understanding the fundamental mechanisms underlying the preimplantation development would greatly enhance our capability to improve reproductive performance of domestic animals or increase the efficiency of assisted reproductive technologies in mammals.