Abstract: Mammalian oocyte meiosis encompasses two consecutive rounds of asymmetric divisions to generate one big egg and，as by-products，two small polar bodies. This asymmetric division is crucial for the oocyte and embryonic development. The interaction between various factors associated with spindle positioning, the formation of myosin ring and extrusion of the first polar body，such as actin-related protein 2/3（Arp2/3）complex，JMY，small GTPase（actin nucleation activation factor），forms the signal pathways regulating the asymmetrical division of oocyte. However，it is found that the aged oocyte shows loss of oocyte cortical polarity，reduction of the nucleation-promoting factors and related regulatory factors and their activities，resulting in the decreased rate of fertilization and then rate of cleavage in aged oocyte. We reviewed the progression of research on loss of asymmetry during meiotic division in aged oocytes.

Key words: Oocytes, Meiosis, Actins, GTP phosphohydrolases, Cortical polarization