Cerebrospinal fluid (CSF) leakage is a major complication during and after transsphenoidal surgery (TSS) for intra- and suprasellar tumors. To prevent postoperative CSF leakage, various surgical techniques have been used, including sellar floor reconstruction with artificial bone grafts. However, some authors have recently reported infections associated with artificial bone grafts. Most cases are associated with bacterial infection, and fungal infection is extremely rare. We present the case of a 53-year-old woman with sphenoiditis caused by Aspergillus infection that developed 8 years after TSS and following local radiation therapy for a non-functioning pituitary adenoma. An artificial bone graft prepared from polymethylmethacrylate was used for sellar floor reconstruction. The patient presented to our department with a complaint of bloody nasal discharge. Magnetic resonance imaging showed that a fungal lump had formed around the bone graft, which had broken into two pieces and dropped out into the sphenoid sinus, without tumor recurrence. Histological examination of an endoscopic biopsy specimen led to a diagnosis of aspergillosis. Subsequent complete removal of both the bone graft and fungal lump resulted in a good postoperative outcome. Although fungal infection is an extremely rare complication after TSS using artificial bone grafts, it should be diagnosed as early as possible, and removal of both the fungal lump and the bone graft should be performed in a timely manner after clinical and radiological confirmation.