en Histopathology Histopathology Original Article Original Article Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa which is considered by the World Health Organization (WHO) as a premalignant condition. One step in malignant development is so called epithelial mesenchymal transition (EMT), a process whereby epithelial cells acquire mesenchymal characteristics. A factor known to induce EMT is the transforming growth factor-β (TGF-β), which uses the Smad proteins as mediators for its signaling. The aim of this study was to compare the expression of Smad 3 in Oral Lichen Planus and normal oral mucosa. This descriptive analytic study was performed on 30 patients with OLP (21 women and 9 men with mean age of 45.23± 2.44 years) and 20 normal oral mucosa (14 women and 6 men with mean age of 46.95± 2.21 years). The samples were studied by immunohistochemical staining. Data were analyzed with paired T-test and Wilcoxon test by SPSS software. Expression of Smad3 in OLP samples and normal oral mucosa was different. This difference was statistically significant (P<0.001). The apparently higher expression of Smad 3 in oral lichen planus compared to normal oral mucosa might help to discuss its higher potential for malignant transition. Oral lichen planus, smad 3, transforming growth factor β 194 198 http://ijmcmed.org/browse.php?a_code=A-10-142-1&slc_lang=en&sid=1 Shima Nafarzadeh 10031947532846003580 10031947532846003580 No Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Babol University of Medical Sciences, Babol, Iran. Samad Ejtehadi 10031947532846003581 10031947532846003581 No Private Dentist, Babol, Iran. Pouyan Amini Shakib pouyanshakib@yahoo.com 10031947532846003582 10031947532846003582 Yes Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Babol University of Medical Sciences, Babol, Iran. Majid Fereidooni 10031947532846003583 10031947532846003583 No Department of Periodontology, Faculty of Dentistry, Babol University of Medical Sciences, Babol, Iran. Ali Bijani 10031947532846003584 10031947532846003584 No Non-Communicable Pediatric Diseases Research Center, Amirkola Hospital, Babol University of Medical Sciences, Babol, Iran.