The author was experienced a case of mucocele in the right maxillary sinus. A 31-year-old Korean male soldier was visited to Capital Army Hospital on Nov. 19, 1969, with chief complaints of nasal obstruction and tender-ness on the right maxillary sinus region. On physical examination, right nasal cavity was completely obstructed by a large bony mass and left nasal cavity was incompletely obstructed due to severe septal deviation to the left. The mass was completely removed by Caldwell-Luc's approach. The post-operative course was uneventful.