The Caldwell-Luc's operation is one of the most common operating procedure for chronic maxillary sinusitis. Many postoperative cheek cysts have seen reported as a latent complication within several years or even far more years later. But, it is very rare whith sequestration in alveolar process forming antro-oral fistula and abscess of alveolar bone. Recently, the authors have experienced a case of postoperative cheek cyst forming antro-oral fistula and report it with a review of literature.