Intracellular distribution of mitochondria varies during development of the oocyte into a fertilizable egg. Here we demonstrate a change in the distribution of mitochondria during oocyte growth and maturation in living mouse oocytes. In growing oocytes, mitochondria concentrated into subcortical and perinuclear areas, whereas it diffusely distributed throughout the cytoplasm in fully-grown oocytes, indicating the variation of mitochondrial distribution in the same G2/M cell-cycle stages. GFP-labeled mitochondria reveal that oocyte maturation involves dynamic reorganization of the mitochondria, and whose process is associated with microtubule organization. These spatio-temporal regulations of mitochondria in oocytes may be important process in the preparation of fertilization and subsequent embryonic development.