Glioblastoma is the most malignant type of brain tumor. Despite recent advances in therapeutic modalities, the prognosis of glioblastoma remains very poor. Recent studies have indicated that RelA/nuclear factor (NF)-κB is consistently activated in human glioblastoma. In this study, we searched for a new treatment modality for glioblastoma, by examining the effects of dehydroxymethylepoxyquinomicin (DHMEQ), a unique small molecule inhibitor of NF-κB. Addition of DHMEQ to cultured human glioblastoma cells inhibited the nuclear translocation of RelA. It also reduced the growth rate of human glioblastoma cells significantly in 6 cell lines and modestly in 3 among 10 cell lines examined. Then, we performed further analyses using 3 sensitive cell lines (U87, U251, and YKG-1). The growth retardation was accompanied by G2/M arrest in vitro. Increased apoptosis was observed in U87 and YKG-1, but not U251 cells after DHMEQ treatment. Then, we tested the efficacy of DHMEQ in chemoprevention through the use of a nude mouse model. Subcutaneous tumors formed by U87 or U251 cells were reduced by ∼40% in size by intraperitoneal administration of DHMEQ started immediately after implantation of the cells. DHMEQ treatment achieved statistically significant improvements in survival curves of mice intracranially implanted with U87 or U251 cells. Histological analysis revealed increased areas of necrosis, increased numbers of collapsed microvessels, decreased nuclear immunoreactivity of RelA, and decreased immunoreactivity of urokinase-type plasminogen activator in the DHMEQ-treated U87 tumor tissues. These results suggest that the targeting of NF-κB by DHMEQ may serve as a promising treatment modality in glioblastoma.