Evi1 is essential for proliferation of hematopoietic stem cells and implicated in the development of myeloid disorders. Particularly, high Evi1 expression defines one of the largest clusters in acute myeloid leukemia and is significantly associated with extremely poor prognosis. Improvement of the therapeutic outcome of leukemia with activated Evi1 is one of the most challenging issues. However, mechanistic basis of Evi1-mediated leukemogenesis has not been fully elucidated. Here we show that Evi1 directly represses PTEN transcription in the murine bone marrow, which leads to activation of AKT/mTOR signaling. In a murine bone marrow transplantation model, Evi1 leukemia showed remarkable sensitivity to an mTOR inihibitor rapamycin. Furthermore, we found that Evi1 binds to several polycomb group proteins and recruits polycomb repressive complexes for PTEN downregulation, which reveals a novel epigenetic mechanism of AKT/mTOR activation in leukemia. Expression analyses and chromatin immunoprecipitation assays using human samples indicate that our findings in mice models are recapitulated in human leukemic cells. Dependence of Evi1-expressing leukemic cells on AKT/mTOR signaling provides the first example of targeted therapeutic modalities that suppress the leukemogenic activity of Evi1. The PTEN/AKT/mTOR signaling pathway and the Evi1-polycomb interaction can be promising therapeutic targets for leukemia with activated Evi1.