We report on two cases of spontaneous CSF otorrhea, which were considered to have been caused by enlarged arachnoid granulation with bone erosion of the posterior fossa. Both cases visited us complaining of severe headache, due to bacterial meningitis. In the first patient, a 68-year-old male, a high resolution CT scan showed a bony defect in the posterior fossa plate in the right temporal bone, where CSF leakage was confirmed during the operation. In the second patient, a 54-year-old female, a bony defect was located in the posterior fossa in the left temporal bone. In both cases, the bony defects were repaired by occlusion with the pedicled temporal muscles after the meningitis had been treated. CSF otorrhea disappeared after the surgery, and has not recurred during the postoperative observation period of 1 to 3 years.