During fertilization, the sperm triggers resumption from the arrest, extrusion of the second polar body and pronuclear formation whose events are collectively acknowledged as ‘oocyte activation‘. In mammalian species up to date, oocyte activation requires fertilization-associated increases in the intracellular concentration of calcium. These periodical rises are referred to as calcium oscillations. Result studies suggest that these calcium oscillations have important role in not only oocyte activation but also development of mammals. We focus on two molecules, phospholipase C zeta (PLCζ;) and inositol 1,4,5-triphosphate receptor (IP₃R) which have important role in regulation of calcium oscillations during fertilization in mammals. In this review, we will discuss present status and future perspective of molecular mechanism during fertilization in mammals.