Pneumococcal meningitis as an overwhelming post-splenectomy infection (OPSI) has a higher risk of neurological complications and is sometimes life-threatening. In acute pneumococcal meningitis, four days of dexamethasone is widely used for the prevention of neurological complications. Herein, we report a 68-year-old woman with the diagnosis of pneumococcal meningitis as OPSI. With adequate antibiotics and dexamethasone, her symptoms gradually improved. However, after dexamethasone withdrawal, her consciousness got worse and got into a coma. Brain magnetic resonance imaging revealed acute cerebral infarctions in the bilateral middle cerebral artery territory with multiple vascular stenoses and hydrocephalus. Vascular stenoses improved by follow-up, suggesting cerebral vasospasm. There were no suggestive findings of cerebral vasculitis. Follow-up cerebrospinal fluid analysis showed remained pleocytosis with no bacteria, which could not suggest meningitis recurrence. Since steroid therapy was rapidly withdrawn, we diagnosed that the cerebral vasospasm was due to the steroid rebound phenomenon. The steroid rebound phenomenon due to the excessive immune response to bacterial microstructures has been reported in pneumococcal meningitis. Especially, the present case was asplenia and the usual dexamethasone use would not adequately suppress the immune response to bacterial microstructures. Since pneumococcal meningitis as OPSI has a higher risk of neurological complications, clinicians should consider longer and more cautious steroid tapering.