Busulfan is a chemotherapy drug that is a cell cycle non-specific alkylating antineoplastic agent (slows the growth of cancer cells). More specifically it belongs to a subclass of alkylating agents known as alkyl sulfonates. It is marketed in the U.S. by GlaxoSmithKline under the brand name Myleran, and has been in clinical use since 1959. Busulfan is also available in an IV formulation marketed as Busulfex by PDL BioPharma, Inc. Its chemical designation is 1,4-butanediol dimethanesulfonate.

Currently, its main uses are in bone marrow transplantation, especially in chronic myelogenous leukemia (CML), where Busulfan is used as a conditioning drug. Busulfan can control tumor burden but cannot prevent transformation or correct cytogenic abnormalities. Though not as common, it may also be used for Chronic Lymphocytic Leukemia (CLL). Busulfan was recently used in a study to examine the role of platelet-transported serotonin in liver regeneration.