A rare case of mucocele of both maxillary sinuses was experienced by author. A 25 year-old man was admitted to the hospital on June, 7, 1969, with chief complaints of the nasal obstruction, hyperrhinorrhea and smelling disturbance for about 6 months. The diagnostic puncture was performed and thick tenacious grayish brown-colored fluid was proved. A good result was obtained after Caldwell-Luc's operation procedure.