Nuclear localization of p53 is essential for its tumor suppressor function. Here, we have identified Parc, a Parkin-like ubiquitin ligase, as a cytoplasmic anchor protein in p53-associated protein complexes. Parc directly interacts and forms a approximately 1 MDa complex with p53 in the cytoplasm of unstressed cells. In the absence of stress, inactivation of Parc induces nuclear localization of endogenous p53 and activates p53-dependent apoptosis. Overexpression of Parc promotes cytoplasmic sequestration of ectopic p53. Furthermore, abnormal cytoplasmic localization of p53 was observed in a number of neuroblastoma cell lines; RNAi-mediated reduction of endogenous Parc significantly sensitizes these neuroblastoma cells in the DNA damage response. These results reveal that Parc is a critical regulator in controlling p53 subcellular localization and subsequent function.