A pterygium is a wing-shaped, fibrovascular conjunctival outgrowth, invading centripetally into the clear cornea, and its incidence is associated with sun exposure (ultraviolet radiation). We investigated whether epithelial-mesenchymal transition (EMT) is involved in the pathogenesis of pterygium. Histopathology showed aberrant fibrotic proliferation beneath the pterygium epithelium, with epithelial processes extending into the stroma. Transmission electron microscopy revealed the dissociation of epithelial cells, which were surrounded by activated fibroblast-like cells. Characteristic downregulation of E-cadherin and intranuclear accumulation of β-catenin and lymphoid-enhancer-factor -1 in pterygial epithelium were also observed by immunohistology. Interestingly, epithelial cells extending into the stroma were positive for both α-SMA/Vimentin and cytokeratin 14. Snail and Slug were immunopositive in the nuclei of pterygial epithelial cells, but not in normal corneal epithelial cells. These results suggested that EMT of basal epithelial cells may play a key role in the pathogenesis of pterygium.