The liver kinase B1 (Lkb1)/AMP-activated protein kinase (AMPK) pathway maintains metabolic homeostasis of cells by promoting catabolism and inhibiting anabolism. Activation of this pathway induces tumor suppressors, including p53, and leads to inhibition of the mammalian target of rapamycin pathway, which often is overactivated in multiple cancers. Thus, the Lkb1/AMPK pathway suppresses cancer by negatively regulating cell proliferation. However, recent studies of mouse hematopoietic stem cells (HSCs) revealed that Lkb1 is critical for maintaining HSCs, rather than limiting their proliferation. Furthermore, the role of AMPK in cancer cells has remained elusive. Outstanding questions concern the role of the Lkb1/AMPK pathway in regulating the metabolism and proliferation of cancer cells within a physiological setting. This review focuses on the function of the Lkb1/AMPK pathway in HSCs and leukemia and provides an overview of the therapeutic strategies aimed at targeting this pathway in cancer.