OKC was classified as cystic lesion by WHO in 1971WHO in & 1991, based on aggressive nature, growth pattern, clinical, histological and immunohistochemical nature in 2005 they again classified it as benign lesion, however in 2017 WHO head and neck pathology reclassified it as cystic lesion. It more commonly occurs in posterior mandible and rarely occurs in maxilla, in this case occurrence of OKC in maxillary posterior region is very rare with distinctive expansion and lifting of maxillary sinus floor without perforating in edentulous area makes it more difficult to detect and justify from residual cyst. Here a 65 years old patient came with chief complaint of pus discharge from upper left posterior region since 7 months, having a small opening in edentulous ridge, which provisional diagnosis was given as residual cyst later after excision of lesion and histopathological analysis it was given as OKC.