Introduction: Epidermal growth factor is a single-chain polypeptide consisting of 53 amino acids with potent mitogenic activity that stimulates the proliferation of a range of normal and neoplastic cells through an interaction with its specific receptor (epidermal growth factor receptor, EGFR). This interaction plays a key role in tumor progression including the induction of tumor cell proliferation. An increased EGFR copy number have been associated with a favorable response to EGFR tyrosine kinase inhibitors therapy. In contrast, K-ras mutations tend to predict a poor response to such therapy. The aim of this study was to determine the correlation between the clinicopathological factors and the up-regulation of EGFR expression and Kras mutations in oral squamous cell carcinoma. Materials and Methods: This study examined the immunohistochemical staining of EGFR, K-ras mutation detection with peptide nucleic acid (PNA)-based real-time polymerase chain reaction (PCR) clamping in 20 specimens from 20 patients with oral squamous cell carcinoma. Results: 1. In the immunohistochemical study of poorly differentiated and invasive oral squamous cell carcinoma, a high level of EGFR staining was observed. The correlation between immunohistochemical EGFR expression and histological differentiation, as well as the tumor size of the specimens was significant (Pearson correlation analysis, significance [r] >0.5, P<0.05). 2. In PNA-based real-time PCR clamping analysis, a K-ras mutation was not detected in all specimens. Conclusion: These findings suggest that the up-regulation of the EGFR may play a role in the progression and invasion of oral squamous cell carcinoma that is, independent of a K-ras mutation.