Little is known concerning promoters or gene therapy specific for malignant glioma. To explore the potential use of midkine promoter in gene therapy for malignant glioma, we constructed a midkine promoter-based conditionally replicating adenovirus (Ad-MK). Midkine was overexpressed in malignant glioma tissues but cyclooxygenase-2 was not. The midkine promoter activity of the 600-bp fragment was 2 orders of magnitude higher in midkine-positive glioma cells than in midkine-negative primary normal brain cells. Ad-MK showed strong oncolytic effects in midkine-positive glioma cells but did not exhibit cytotoxicity in midkine-negative primary normal brain cells. The cell-killing effect was evident in E3-intact Ad-MK more than in E3-deleted Ad-MK. In an animal experiment, Ad-MK completely eradicated midkine-positive glioma xenografts. These findings indicate that midkine promoter-based conditionally replicative adenovirus might be a promising new modality of gene therapy for malignant glioma.