INTRODUCTION: Oral cancer is the sixth most prevalent form of cancer, with oral squamous cell carcinomas (OSCCs) exhibiting the highest morbidity of all head and neck cancers. However, the specific metastatic mechanism is not yet clear. MicroR-300 (miR-300) has been identified as a critical regulator in tumor development. In this study, we focused on the roles of miR-300 in regulating epithelial-mesenchymal transition (EMT) in OSCC. METHODS: The surgical specimens from cases of OSCC (N=120) were collected, and the miR-300 expression was tested and the results were analyzed for possible correlations with clinical characteristics, and the prognostic significance was assessed by Kaplan-Meier analysis and Cox proportional hazards regression in OSCC patients. In addition, the proliferation and invasion of OSCC cells were evaluated after transfection of miR-300 mimics or inhibitor. At last, the role of miR-300 in EMT was investigated. RESULTS: The results showed that miR-300 levels were significantly lower in patients with OSCC than in controls and miR-300 levels in patients with OSCC were significantly associated with TNM classification. Kaplan-Meier analysis indicated that miR-300 with lower level had significantly decreased overall survival and disease-free survival of OSCC patients. In multivariate analysis, TNM stage, miR-300 expression and tobacco usage were the independent prognostic factors for overall survival and disease-free survival in OSCC. Moreover, in vitro experiments showed that miR-300 could inhibit the proliferation and invasion of OSCC cells. More importantly, miR-300 could inhibit the EMT process. In addition, we found that ET-1 could inhibit the expression of miR-300. CONCLUSION: Our findings indicated that miR-300 could suppress metastasis of OSCC by inhibiting EMT. The present study indicates that miR-300 is a potential therapeutic agent for OSCC.