The purpose of this study was to evaluate the role of c-fos and c-jun expression in the oral squamous cell carcinoma and ameloblastomas. For this study, 12 subjects diagnosed as squamous cell carcinoma and 7 subjects of ameloblastomas referred to the Dept. of Oral Path. School of Dentistry, Kyung Hee University, 2 subjects of normal oral mucosa without any inflammatory changes were used as experimental, control groups respectively. All the tissues ; experimental and control group were fixed in neutral formalin solution and embedded in paraffin, serial tissue section were made 5㎛ in thickness and processed in the standard way for immunohistochemical method, using primary and secondary antibodies, for c-fos (Anti-c-fos protein, rabbit polyclonal kit at 1:100 dilution), c-jun( anti-c-jun protein, rabbit polyclonal at 1:100 dilution), all BioGenex U.S.A. made, followed by the Streptavidin - Horse Radish Peroxidase(InnoGenex, Human-Avidin kit) application, counter stained with Mayer's hematoxylin stain method, mounted. And examined under the biologic microscope, with the criteria-(no epithelial stain), +(weak or focal epithelial stain), ++(moderate or focal intensive epithelial stain), +++(intense generalized epithelial staining) for the epithelial, and connective tissue component in squamous cell carcinomas, ameloblastomas and normal mucosal epithelium on each. Attained results as follows ; 1. In oral mucosa, c-fos and c-jun intensely expressed on the all cell layers except on the basal layer. Intense reaction is noted in the c-jun than in the c-fos. and a few cells with positive cytoplasm, negative nuclear are scattered in all layer. 2. The response to c-fos in ameloblastomas, is various according to the histological type, but intense resposes are nodted in nuclear and cytoplasm on the tall columnar cells at the periphery of the follicles compare to that on the stellate cells. 3. The respone to c-fos in squamous cell carcinoma, intense reaction is noted in cytoplasm and nuclei of the tumor cells in well differentiated, poorly differentiated type. 4. The response to c-jun in ameloblastoma, it is noted that moderate respone in nuclear and cytoplasm, at the tall columnar cells at the periphery of follicular or plexiform type but intense respone was notes on the columnar cells, and stellate cell in cytoplasm and nuclear of acanthomatous type. 5. The respon to c-jun in squamous cell carcinoma, it is noted that intensive responses only in cytoplasm in well differentiated type, but intensive responses in nuclei and cytoplasm in the poorly differentiated type are revealed. Intensive responses on c-fos, c-jun were noted on the high atypical cells. This results suggest that c-fos and c-jun may be affected to the reactivation on growth and development of the squamous cell carcinoma.