---

Abstract
Background and Aim: Oral squamous cell carcinoma (OSCC) develops through a series of precancerous stages manifested at the microscopic level as epithelial dysplasia and Ki-67 gene may play an important role in this course. The aim of this study was to comparative investigation  of Ki67 expression in oral epithelial dysplasia and OSCC by immunohistochemistery technique .
Materials and methods: Ki67 expression was evaluated in paraffin blocks of 15epithelial hyperplasia with no dysplasia (A group), 15 epithelial dysplasia (B group) including 7 mild epithelial dysplasia (B1subgroup) and 8 sever epithelial dysplasia (B2 subgroup), 15 OSCC (C group) including 7 well differentiated OSCC (C1 subgroup) and 8 poorly diffrentiated OSCC(C2 subgroup).
Results: There was a significant difference in Ki67 expression based on quantitative and smiquantitative analysis between the three groups and Ki67-positive cells were significantly higher in C group than B group. A positive significant difference was observed between Ki67-positive cells and increasing grade of dysplasia ( P<0/001 ).However, Ki67 expression was not significant different between histopathological grades of OSCC ( p=0/064) .
Conclusion: Ki-67 may represent a significant marker to recognize evolution of precancerous diseases in the oral cavity, a reliable marker to improve identification of the degree of dysplasia and for the prediction of malignant change in these lesions.