In recent years, there have been considerable research advances on the antileukemic mechanisms of the antidiabetic drug metformin. Our current studies have shown that metformin suppresses cell viability, induces apoptosis, and downregulates the mTORC1 signaling pathway both in the Ph+ALL cell line and primary blasts from Ph+ ALL patients, as well as the CML cell lines K562 (imatinib-sensitive) and K562R (imatinib-resistance). We have also shown that metformin activates the ERK pathway in Ph+ALL cells, SUP-B15, a side effect that can be overcome by U0126 (MEK1/2 inhibitor) or imatinib. Moreover, this activation of ERK signaling in SUP-B15 induces autophagy. Inhibition of the autophagic process by 3-MA, promoting the death of these cells, suggests that autophagy may be a cytoprotective factor in cell survival after metformin treatment. Finally, metformin is shown to potentiate the anticancer efficacy of imatinib in Ph+ALL and CML cells, resensitizing the CML imatinib-resistance cells to imatinib. Overall, our data suggest that metformin represents a promising and attractive agent for Ph+ALL or CML therapy.