We treated a 57-year-old woman for ranula. After aspirating the cyst's contents, we administered 0.1 KE/ml of OK-432 via local injection. One month later, the cyst had still persisted, so we repeated the procedure. After 2 weeks, the ranula began to shrink markedly, and at 4 weeks it had almost disappeared. No recurrence of the ranula was observed during the subsequent 1 year of follow-up. Following each injection, the patient developed transient fever and local swelling but no serious complications. Our experience suggests that OK-432 injection is an effective treatment for ranula. However, because this treatment causes the cyst to collapse rather than disappear completely, patients should be regularly monitored over the long term.