Abdulazeem  A Gadad¹ , Una M El-Shinnawi² , Nagla M Salama³ 1-BDS, Faculty of Dentistry, Tripoli University, Libya 2-Professor of Oral Medicine and Periodontology Facultofdentistry, Mansoura University. 3-Assistant Professor of Oral Pathology Faculty of Dentistry, Mansoura University Abstract: Background :oral lichen planus (LP) is a chronic inflammatory disease of probable immune-based etiology. The pathogenesis of LP is unclear, but apoptotic changes in epidermal (epithelial) cells have been reported. Destruction of the basal cell layer is observed and many changes in cell proliferation, cell repair and cell death occur in the injured mucosal epithelium. Oral squamous cell carcinoma accounts for   90% of all oral cancers. It may affect any anatomical site in the mouth, but most commonly the tongue and the floor of the mouth. It usually arises from a pre-existing potentially malignant lesion, and occasionally de novo; but in either case from within a field of precancerized epithelium. The use of tobacco and betel quid, heavy drinking of alcoholic beverages and a diet low in fresh fruits and vegetables are well known risk factors for oral squamous cell carcinoma                                        Aim of the study:the aim of the present study is to evaluate the expression of Bax and bcl-2 as a diagnostic immunohistochemical marker for the different varieties of Oral Lichen Planus and Oral Squamous Cell Carcinoma.                                                                                Material and methods:This study was conducted on 40 subjects (20 paraffin specimens  with oral lichen planus , 20 paraffin specimens  with oral squamous cell carcinoma) . We used immunohistochemistry staining method for assessing bax and bcl-2 expression in epithelial layers.                       Results : the bcl2  expression were significantly higher in  erosive  oral lichen planus compared to reticular oral lichen planus ( p= 0. 4) while Bax expression showed significant decrease in erosive type compared to reticular type ( p= 0.03) .On the other hand  the there were significant increase of bcl2 percentage of expression from well differentiated , moderately differentiated to poorly differentiated  , there was  significant difference at ( P = 0.001), meanwhile there is significant decrease of bax percentage of expression from well differentiated OSCC  , moderately differentiated OSCC to poorly differentiated OSCC there  was significant  difference at ( P = 0.001). Conclusion:  Patients with high Bax expression had better disease specific prognosis compared with those who had low Bax expression,        For   Bcl-2 expression the opposite correlation was found, with      significantly poorer disease specific prognosis for patients with   high Bcl-2 expression, bax and bcl2 can be used as a diagnostic value for oral lichen planus and oral squamous cell carcinoma