Objective: To check for a possible relation between the expression of BMI-1 among two different odontogenic lesions; ameloblastoma and dentigerous cyst known for different biological behavior. Materials and Methods: The study was conducted on 14 formalin-fixed paraffin-embedded blocks (ameloblastoma (Am) group: seven blocks and dentigerous cyst (DC) group: seven blocks). These blocks were collected from archived files of the Department of Oral Pathology, Faculty of Dentistry, Mansoura University.  Immunohistochemically (IHC), the BMI-1 polyclonal antibody expression in the retrieved sections was investigated. A computerized method was used to compare the IHC staining intensity between both groups. Results: The difference in the intensity of immunoreactivity to BMI-1 in two different studied groups was statistically non-significant to gender, age, and site (P > 0.05). The Am group showed significantly higher expression of BMI-1 than the DC group (P < 0.0001). Conclusions: BMI-1 is thought of as a useful marker probably delineating the variation in the biological behavior of Am and DC.