We describe a novel function of parkin, a RING protein, which is elaborately involved in mitochondrial biogenesis. Parkin was located within the mitochondrial organelle of proliferating cells. Anti-proliferative treatments released parkin from mitochondria to cytosol. Results of pharmacological treatments indicate that parkin was released from mitochondria when permeability transition pore was opened. The extra-mitochondrial localization was also observed in differentiated cells. In proliferating cells, transcription and replication of mitochondrial DNA was enhanced by parkin overexpression and attenuated by parkin suppression with siRNA. Parkin was associated with mitochondrial transcription factor A (TFAM) and enhanced TFAM-mediated mitochondrial transcription. These results indicate that parkin is involved in the regulation of mitochondrial transcription/replication other than the ubiquitin-mediated protein degradation system in proliferating cells.