Glioblastomamultiforme (GBM) is the most common malignant and aggressive primary tumor of the brain in adults and characterized by a heterogeneous population of cells that are genetically unstable, highly infiltrative, angiogenic, and resistant to chemotherapy. Considerable efforts being devoted to identifying the molecular basis of resistance in GBM and exploring novel therapeutic targets that may improve overall survival. Several independent DNA repair mechanisms that normally safeguard genome integrity can facilitate drug resistance and cancer cell survival by removing chemotherapy- induced adducts. The recent data suggest that the most important mechanism of resistance to alkylating agents is the DNA repair enzyme O6-methylguanine methyltransferase (MGMT). Although, the treatment failure is a result of a number of causes, but currently, it has been demonstrated that a highly tumorigenic subpopulation of cancer cells called glioblastoma stem cells (GSCs) display relative resistance to radiation and chemotherapy. In fact, GBM stem cells express high levels of MGMT and this may account for GBM resistance following chemotherapy. GSCs also contribute to tumor growth through the stimulation of angiogenesis, which has been shown to be a useful therapeutic target in the treatment of recurrent or progressive malignant gliomas. In this review, we summarize the chemoresistance mechanisms of GBMs (to alkylating agents), with a special focus on the role of cancer stem cells.