The promyelocytic leukemia (PML) tumor suppressor protein accumulates in PML nuclear bodies (PML-NBs), and can induce growth arrest, cellular senescence and apoptosis. PML has also been localized in the cytoplasm, although its function in this localization remains elusive. A general property of primary cancers is their high glycolytic rate which results from increased glucose consumption. However, the mechanism by which cancer cells up-regulate glycolysis is not well understood. Here, we have shown that cytoplasmic PML (cPML) directly interacts with M2-type pyruvate kinase (PKM2), a key regulator of carbon fate. PKM2 determines the proportion of carbons derived from glucose that are used for glycolytic energy production. Over-expression of PML-2KA mutant in the cytoplasm, which was generated by mutagenesis of the nuclear localization signals of PML, in MCF-7 breast cancer cells suppressed PKM2 activity and the accumulation of lactate. PKM2 exists in either an active tetrameric form which has high affinity for its substrate phosphoenolpyruvate (PEP) or a less active dimeric form which has low affinity for its substrate. Over-expression of PML-2KA suppressed the activity of the tetrameric form of PKM2, but not the dimeric form. Our findings suggest that cPML plays a role in tumor metabolism through its interaction with PKM2.