One of recent advances of mammalian fertilization is the understanding of the molecular basis of fertilization. Several proteins localized in sperm nucleus or on sperm surface are necessary for the fertilization process. Protamines, sperm nuclear proteins, are required for normal sperm function that leads to fertilization. Fertilin and cyritestin are sperm surface proteins and essential for sperm-egg binding. Fertilin is also required for sperm transport in the female reproductive tracts. Metalloproteses on sperm plasma membrane are found to play a role in sperm-egg fusion. The functional analysis of these proteins provides a new insight into the molecular mechanisms underlying mammalian fertilization and male fertility.