BACKGROUND: Oral squamous cell carcinoma (OSCC) is the most common head and neck malignancy with a low five-year survival rate. ATP-binding cassette subfamily B member 5 (ABCB5) has been linked to tumorigenesis. However, its role in inducing OSCC remains unclear. METHODS: Quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot, and immunocytochemistry (ICC) were performed to examine the level of ABCB5 in OSCC (CAL27 and HSC-3) and human oral keratinocyte (HOK). ABCB5 was knocked down in CAL27 cells using ABCB5-specific small interfering RNA (ABCB5 siRNA), and its contribution to migration, invasion, and epithelial-mesenchymal transition (EMT), a process by which epithelial cells lose their tight junction and acquire an increased migratory and invasive phenotype resembling that of mesenchymal cells, were evaluated by three-dimension and transwell migration and invasion assays, qRT-PCR and ICC. An in vivo OSCC model was established using 4-nitroquinoline-1-oxide (4NQO), a carcinogenic chemical that is commonly used to develop OSCC by destroying DNA synthesis and oxidative stress. Pathological alterations, ABCB5, and EMT markers were evaluated by H&E staining, immunohistochemistry, and qRT-PCR. RESULTS: ABCB5 was significantly upregulated in CAL27 and HSC-3 cells as compared to HOK. Knockdown of ABCB5 significantly reduced the number of migrated and invaded CAL27 cells, accompanied by the significantly increased E-cadherin and decreased Vimentin and N-cadherin under Transforming growth factor β (TGF-β) treatment. In vivo, as OSCC advanced, a notable rise in the expressions of ABCB5, N-cadherin, and Vimentin, while a statistical decrease in E-cadherin was demonstrated. CONCLUSION: ABCB5 promotes the migration, invasion, and EMT of OSCC. ABCB5 might be a new biomarker and potential therapeutic target for OSCC.