In vitro maturation (IVM) of oocytes is an important part of assisted reproduction (ART), having a wide range of research and clinical applications. IVM is usually used to generate mature oocytes not only in human infertility treatment but also in animal reproduction. However, it is generally accepted that the developmental competence of embryos produced using IVM oocytes is lower than that of their in vivo counterparts, probably owing to an inappropriate status of the cytoplasm. To understand how oocytes acquire the developmental competence during meiotic maturation, we conduct researches focused on the chromosome behavior, changes of gene expression and mitochondrial functions in oocytes.