A 27-year-old pregnant woman was scheduled for cesarean section under spinal anesthesia. Although there was no trouble in three repeated spinal punctures, the anesthetic effect was insufficient. Then we changed anesthetic management to general anesthesia. There was no postoperative neurological complications related to spinal anesthesia. Postoperatively, spinal arachnoid cyst was found by MRI. The cyst was thought to have caused insufficient analgesic effect of spinal anesthesia in this patient.