Epithelial-mesenchymal transition (EMT) enhances the invasive ability, providing an explanation for the mechanism of tumor metastasis. The stiffness of the stromal extracellular matrix collagen can regulate the epithelial cell growth and migration in oral epithelial dysplasia (OED) and oral squamous cell carcinoma (OSCC). Objectives: to study the epithelial expression of Vimentin as a marker for EMT and to elucidate the nature of collagen in OED and OSCC and finally to correlate EMT to collagen quality in these lesions. Material and methods: the area fraction of immunohistochemical epithelial expression of Vimentin and color polarization of picrosirius red stained collagen fibers were detected in ten specimens of each grade of OED and OSCC as well as normal oral mucosa followed by statistical analysis. Results: a statistically significant increase in the median area fractions of epithelial Vimentin expression and yellow-green fibers were detected as the grade of OED and OSCC progressed. Spearman's correlation coefficient revealed a statistically significant direct correlation between epithelial Vimentin expression and yellow-green fibers in these lesions. Conclusion: there was a statistically significant increase in EMT and decrease in the collagen quality with the advance of OED and dedifferentiation of the neoplasm. The significant inverse correlation between EMT and collagen quality indicates the role of EMT in stromal collagen quality in these lesions and aid in their prognosis.