Background: The pathogenesis of oral squamous cell carcinoma is very complex and prognostic markers are difficult to find in these carcinomas of which the different subtypes have varying malignant potential. The study was conducted to investigate the immunohistochemical expression of MMP-9 in epithelial dysplasia and different grades of oral squamous cell carcinomas and to study the possible correlation between increased MMP-9 immunoexpression and progression of epithelial dysplasia in the studied dysplastic and OSCC lesions. Materials and methods: thirty paraffin blocks of OSCC (10 well differentiated, 10 moderately differentiated and 10 poorly differentiated) and ten paraffin blocks of epithelial dysplasia were immunohistochemically stained with MMP-9 antibody. ANOVA and Tukey's tests were used for the statistical analysis. Results: All cases of OSCC express MMP-9 with variable cellular localization. There was a significant difference in the expression of MMP-9 between the different grades of OSCC cases. Conclusions: Oral squamous cell carcinomas express MMP-9 with variable levels and cellular localization, consisting an important marker of biological behavior in these tumors. Further investigations are recommended to study the MMP-9 effect on invasion and metastasis of OSCC in order to correlate its expression with clinical outcome.