A 45-year-old man presented with a rare case of glioblastoma associated with intratumoral abscess formation manifesting as headache and vomiting after an appendectomy. Computed tomography and magnetic resonance imaging demonstrated a ring-enhanced lesion mimicking malignant glioma. Craniotomy and tumor removal were performed. Abscess formation within the intra-axial tumor was found intraoperatively. Histological examination revealed glioblastoma with abscess, and the etiological agent was anaerobic Gram-negative bacilli. The suspected route of microbial migration and colonization in this tumor was bacteremia from appendicitis.