A 13-year old boy was referred to the dept. of Oral Surgery in Dental Infirmary of S.N.U. and followed by thorough examination, was diagnosed as an odontogenic cyst in maxilla. The author has reported this case because it is a rare one that the expansion of two different preoccurred odontogenic cysts formed a large fused-type cystic cavity and complete enucleation of the mass under general anesthesia brought satisfactory results.