Mitochondria are highly dynamic organelles in eukaryotic cells. Although the role of mitochondria in metabolism, ATP production and apoptosis is more widely recognized, alterations in mitochondrial morphology and abundance are also important for cellular functions. Here we investigated mitochondrial dynamics in synchronized HeLa cells in which the major stages of the cell cycle of the observed cells were resolved by staining phosphorylate histones H1 and H3, and showed that mitochondria exist as filamentous network structures throughout the cell cycle progression, changing their morphology, distribution, and abundance. The current results suggest that mitochondrial condensation occurred at prophase is required for the proper progression of mitochondrial division.