Abstract: Reprogramming in mammalian cell development is currently a scientific hotspot of cell biology，translational medicine，and so on，due to its extensive prospect of application in somatic cell nuclear transplantation（SCNT），induced pluriponent stem cell（iPS） and regenerative medicine. Epigenetic modification is major reprogramming，including DNA methylation，histone post-translational modifications，genomic imprinting，non-coding RNAs，and so on，which regulates genome expression via different mechanisms. For instance, the development and maturation of oocyte is closely associated with the de novo methylation of genome, demethylation of meiosis genes, post-translational histone modifications, etc. Besides, the oocyte provides an optimal reprogramming environment for the demethylation and other reprogramming processes of male pronucleus genome via their reciprocal interactions. The reprogramming in oocyte development and further fertilization，as well as its significance in embryonic development, was reviewed, and the effect of oocyte′s environment on the reprogramming of penetrated male pronucleus during natural fertilization was also discussed.

Key words: Oocytes, Nuclear reprogramming, Fertilization, Embryonic development, Male pronucleus