The p53 tumor suppressor gene is an important target for the gene therapy of cancers, and clinical trials targeting this gene have been conducted. Some cancers, however, are refractory to p53 gene therapy. Therefore, it has been combined with other therapies, including chemotherapy and radiotherapy, to enhance the cytopathic effect of p53 induction. The p33ING1 gene cooperates with p53 to block cell proliferation. In this study, we investigated whether adenovirus (Adv)-mediated coinduction of p33ING1 and p53 enhances apoptosis in glioma cells (U251 and U-373 MG), which showed no genetic alterations but low expression levels of p33ING1. Although the single infection of Adv for p33ING1 (Adv-p33) at a multiplicity of infection (MOI) of 100, or Adv for p53 controlled by myelin basic protein (MBP) promoter (Adv-MBP-p53), a glioma-specific promoter, at a MOI of 50, did not induce apoptosis in U251 and U-373 MG glioma cells; coinfection of Adv-p33 and Adv-MBP-p53 at the same MOIs induced drastically enhanced apoptosis in both cell lines. Apoptosis was not induced in NGF-treated PC-12 cells infected with a high MOI (300) of Adv-p33 nor in those coinfected with Adv-p33 (100) and Adv-MBP-p53 (50). Coinfection of Adv-p33 and Adv-MBP-p53 demonstrated morphological mitochondrial damage during the initial stage of apoptosis, which likely led to apoptotic cell death. Our results indicate that this coinfection approach can be used as a modality for the gene therapy of gliomas, sparing damage to normal tissues.