<p>Oral squamous cell carcinoma (OSCC) is the most common aggressive malignancy of the head and neck squamous cell carcinoma (HNSCC) subtype. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by target degradation or inhibition of translation. miR-21-5p is a multifaceted miRNA found to be overexpressed and acts as a potent oncogene, regulating various cellular pathophysiology, such as cell proliferation, invasion, migration, and apoptosis, in many cancers, including OSCC. Despite its established involvement in OSCC progression, the upstream regulators of miR-21-5p and its downstream targets are still not completely elucidated. Transforming growth factor-beta (TGF-β) is a cytokine that shows a paradoxical role in diverse diseases, including OSCC. TGF-β exerts oncogenic effects in OSCC, shown by the induction of mesenchymal markers, which may account for the metastatic potential of OSCC. Through small RNA sequencing of SCC-25 cells treated with TGF-β, we identified numerous miRNAs that were induced in OSCC. Further, this study confirms the positive correlation between the TGF-β pathway and miR-21-5p induction, in which miR-21-5p is transcriptionally induced by the SMAD-mediated TGF-β signaling pathway. Mechanistically, TGF-β-induced miR-21-5p exerts its oncogenic effects in OSCC by post-transcriptionally suppressing its target, the transcription factor KLF5 (Kruppel-like factor 5). Loss-of-function studies on KLF5 confirmed its tumor suppressive role in SCC-25 and SCC-9 OSCC cells. Taken together, our study reports for the first time the existence of a TGF-β/miR-21-5p/KLF5 regulatory axis in OSCC, which could potentially be of therapeutic value. This article aligns with SDG 3 (Good Health and Well-Being) of the UN Agenda for Sustainable Development.</p> Graphical abstract <p></p>