Egg activation is a crucial step that initiates embryo development upon breaking the meiotic arrest. In mammalian, egg activation is accomplished by fusion with sperm, which induces the repeated intracellular - increases ( oscillation). Researches in mammals support the view of the oscillation and egg activation is triggered by a protein factor from sperm that causes release from endoplasmic reticulum, intracellular store, by persistently activation of phosphoinositide pathway. It represents that the sperm factor generates production of inositol trisphosphate (). Recently a sperm specific form of phospholipase C zeta, referred to as PLCZ was identified. In this paper, we confer the evidence that PLCZ represent the sperm factor that induces oscillation and egg activation and discuss the correlation of PLCZ and infertility.