The prognosis of patients with glioblastoma is extremely poor despite multimodal treatments including surgery, chemotherapy and radiotherapy. Recently, the alkylating agent, temozolomide (TMZ) has been shown to improve survival in patients with malignant gliomas, including those with glioblastoma in some clinical studies, and has become one of the standard modalities for treatment of newly diagnosed and recurrent malignant gliomas. The epigenetic silencing of the DNA repair enzyme O(6)-methylguanine-DNA-methyltransferase (MGMT) is the strongest predictive marker for favorable outcome in patients treated with TMZ. However, it remains to be determined how patients with tumors lacking MGMT promoter methylation should be treated. Moreover, even patients with TMZ-sensitive glioblastoma cannot avoid eventual recurrence. In this article, we review the mechanism of the effect of TMZ on tumor cells and resistance to TMZ, and provide an overview of the current management and trials for patients with glioblastoma.