Ribavirin, a nucleic acid analog, has been employed as an antiviral agent against RNA and DNA viruses and has become the standard agent used for chronic hepatitis C in combination with interferon-α2a. Furthermore, the potential antitumor efficacy of ribavirin has attracted increasing interest. Recently, we demonstrated a dose-dependent antitumor effect of ribavirin for seven types of malignant glioma cell lines. However, the mechanism underlying the antitumor effect of ribavirin has not yet been fully elucidated. Therefore, the main aim of the present study was to provide further relevant data using two types of malignant glioma cell lines (U-87MG and U-138MG) with different expression of MGMT. Dotted accumulations of γH2AX were found in the nuclei and increased levels of ATM and phosphorylated ATM protein expression were also observed following ribavirin treatment (10 µM of ribavirin, clinical relevant concentration) in both the malignant glioma cells, indicating double-strand breaks as one possible mechanism underlying the antitumor effect of ribavirin. In addition, based on assessements using FACS, ribavirin treatment tended to increase the G0/G1 phase, with a time‑lapse, indicating the induction of G0/G1-phase arrest. Furthermore, an increased phosphorylated p53 and p21 protein expression was confirmed in both glioma cells. Additionally, analysis by FACS indicated that apoptosis was induced following ribavirin treatment and caspase cascade, downstream of the p53 pathway, which indicated the activation of both exogenous and endogenous apoptosis in both malignant glioma cell lines. These findings may provide an experimental basis for the clinical treatment of glioblastomas with ribavirin.