Phosphatidylinositol 3-kinase (PI3K), a heterodimeric lipid kinase, is a key enzyme in signal transduction from various stimuli to downstream pathways that elicit diverse responses involving growth, proliferation, survival, differentiation, and metabolism in many cellular systems. Activated PI3K generates phosphatidylinositol-3,4,5-triphosphate, which recruits phosphatidylinositol-dependent kinase 1 (PDK1) and Akt serine/threonine kinase at the plasma membrane, resulting in activation of Akt. In turn, Akt activates multiple downstream targets, most notably the mTOR pathway. There is abundant evidence implicating the PI3K/Akt/mTOR pathway in the development and progression of a variety of tumors including hematologic neoplasms. Therefore, this pathway is considered a critical target for cancer therapy. We review the regulatory mechanisms of the PI3K/Akt/mTOR signaling pathway and the role of this pathway in oncogenesis of hematological malignancies.