Background: Infectious basilar artery (BA) aneurysm has been occasionally reported to be generated from meningitis following transcranial operation. However, infectious BA aneurysm formed by intracranial infection after endoscopic endonasal operation has never been reported. Case presentation: A 53-year-old man who was diagnosed with suprasellar region meningioma received tumor removal via endoscopic endonasal approach. After operation he developed cerebrospinal fluid (CSF) leak and intracranial infection. The patient ultimately recovered from infection after anti-infective therapy, but a large fusiform BA aneurysm was still formed and ruptured in a short time. Interventional and surgical measures were impossible due to the complicated shape and location of aneurysm and state of his endangerment, therefore, conservative anti-infective therapy was adopted as the only feasible method. Unfortunately, the aneurysm did not disappear and the patient finally died from repeating subarachnoid hemorrhage (SAH). Conclusion: Though extremely rare, it was emphasized that infectious aneurysm can be formed at any stage after transnasal surgery, even when the meningitis is cured. Because of the treatment difficulty and poor prognosis, it was recommended that thorough examination should be timely performed for suspicious patient to make correct diagnosis and avoid fatal SAH. © 2020 The Author(s).