Since the first attempt to fertilize mammalian eggs in vitro by Schenk(1878), many attempts have been made to fertilize mammalian eggs by the adition of sperms outside of the body. How -ever, the incomplete conception of the critea of fertilization, the lack of confirmation of the results, and the likelihood of fertilization in vitro are not acceptable yet. Biologically, fertilization is a physiological progress, which starts with the penetration of sperm into the cytoplasm of the egg and includes the subsequent formation, development and syngamy of the male and female pronuclei until the union of material and paternal genetic materials. The criteria as evidence of fertilized eggs into may be bnormally fertilized or may not be fertilized at all. Robert Edward(1969)in England reported that good number of ovarian oocytes were matured in follicular fluid and possibly fertilized in chemically defined media of Barister`s salt solution by sperm. However, the validity and reliability of the supposedly successful in vitro fertilization of this human experiment have been questioned from the point of view of the cytological criteria for the physiological mechanism involved in mammalian fertilization, particularly the reaction between sperm and eggs, the mechanism of sperm capacitation, the mechanism of sperm penetration, the behavior of pronuclei, and the integration of paternal and maternal materials within the egg.