Objective To clarify the relationship between oocyte maturation and mitochondria distribution by investigating the distribution of mitochondrial in immatured and matured human oocytes. Methods Both immatured and matured oocytes were stained by Mito Tracker Green FM. After they were fixed by paraformaldehyde, the distribution of mitochondria was observed using laser scanning confocal microscope. Results Three mitochondria distribution patterns were identified: peripheral, semiperipheral and evenly diffused. 64.10%(50/78) of the GV oocytes presented a peripheral distribution of mitochondria. 45.16%(28/62) of the MI oocytes had maintained the peripheral distribution,while 38.71%(24/62) presented a diffused status. After in vitro maturation, 75.47%(80/106)of the oocytes displayed an evenly diffused type of distribution. Compared with the oocytes matured in vitro,the most marked feature of oocytes matured in vivo was that mitochondria distributed in the central region. Staining in the center of the oocyte was stronger than that in the peripheral region. Conclusion There were obvious changes in the distribution of mitochondria in human oocytes before and after maturation.The chief distribution pattern of mitochondria was changing fro