The progression of tumor depends on the level of Bcl-2 which protects the cells from undergoing apoptosis, and its level should be more than the level of the death inducer. So, our Aim: To investigate chemopreventive effect of olive oil in epithelial alteration which induced in hamster buccal pouch. Methods: Epithelial dysplasia will occur by the application of DMBA on alternative days for 8 weeks on hamster buccal pouch. Hematoxylin and Eosin (H&E) and Streptavidin-biotin immunoperoxidase staining techniques were used to detect the expression of Bcl-2 in three groups (G1 negative control or normal group, G2 DMBA group and G3 olive oil chemoprevention group). Evaluation of the immunostaining was done by using computer image analyzer system. Results: H & E stained histological section in G1 with normal mucosa of HBP intact, and continuous epithelium of thin keratinized stratified squamous epithelium while in G2 there were incidence of severe epithelial dysplasia with hyperkeratosis & G3 reduced dysplasia incidence and severity as compared to G2. Bcl-2 immunohistochemical expression in G1 in basal & suprabasal layers while in G2 & G3 located in all epithelial layers with statistically highly significant difference (P<0.01) in means values of Bcl-2 expression among (G2>G1, G3) and (G3>G1). Conclusion: Olive oil plays an important role in reduction and prevention of transformation of normal oral epithelium into epithelial dysplasia. The liquid form of olive oil may be considered as a new line of chemoprevention in oral dysplasia and the Bcl-2 expression evidenced this reduction of abnormality in epithelial dysplasia.