Primary intraosseous squamous cell carcinoma (PIOSCC) derived from an odontogenic keratocyst (OKC) is a rare malignant neoplasm of the jaws, which is locally aggressive with quite poor prognosis. The incidence of carcinomas arising in odontogenic cysts was reported to be approximately 1–2/1000. The number of well-documented cases of PIOSCC ex OKC is extremely small; hence, no sufficient incidence data are available in the literature. Overall, the survival rate of an individual, which is a period of two years, is very poor, and this can be attributed to the delayed diagnosis. But knowledge of the histopathological and immunohistological features of PIOSCC allows accurate and early diagnosis of the lesion so that an early and appropriate treatment can be instituted for better prognosis. The following report describes an extremely rare case of PIOSCC of the mandible derived from an OKC in a 20-year-old female patient.