Significance SIRT6 (sirtuin 6) is a member of the highly conserved sirtuin family of NAD + -dependent deacetylases. SIRT6 regulates diverse cellular processes including tumorigenesis. However, the role of SIRT6 deacetylase activity in its tumor-suppressor functions is not well understood. Here we report that SIRT6 deacetylates nuclear PKM2 (pyruvate kinase M2). PKM2 is a glycolytic enzyme with nonmetabolic nuclear oncogenic functions. SIRT6-mediated deacetylation results in PKM2 nuclear export in an exportin 4-dependent manner. As a result of SIRT6-mediated deacetylation, PKM2 nuclear protein kinase and transcriptional coactivator functions are abolished. Thus SIRT6 suppresses PKM2-dependent cell proliferation and tumorigenesis. Taken together, our findings demonstrate the pivotal role of deacetylase activity in SIRT6 tumor-suppressor functions and delineate a mechanism of PKM2 nuclear export.