Mammalian sperm acquire the capacity for motility and fertility during transit through the epididymis. Such functional maturation of sperm is suggested to be partly supported by the epididymal secretory proteins that interact with the sperm surface. We have purified several proteins, which are synthesized and secreted from the specific regions in epididymis, and cloned their CDNAS. In this paper, roles of those proteins involved in the sperm maturation in epididymis have been discussed in connection with the functional differentiation of epididymis.