The autophagy-related gene Beclin-1 is critical in the regulation of tumourigenesis and progression, but its role in oral tongue squamous cell carcinoma (OTSCC) has not yet been reported. This study aimed to investigate Beclin‑1 expression and its significance in OTSCC. Beclin‑1 expression was assessed by reverse transcription‑quantitative polymerase chain reaction or western blot analysis in 14 OTSCC tissues and matched adjacent noncancerous tissues as well as in 5 OTSCC cell lines and a normal tongue epithelial cell line. Beclin‑1 protein expression was examined by immunohistochemistry in 133 OTSCC specimens, and the correlation between Beclin‑1 expression and clinicopathological features was investigated. Furthermore, MTT and colony formation assays were performed to investigate the effect of Beclin‑1 on the proliferation and clonogenicity of OTSCC cells. It was demonstrated that Beclin‑1 expression was significantly decreased in the majority of the 14 OTSCC tissues and the 5 OTSCC cell lines relative to the matched non‑cancerous tissues and the normal tongue epithelial cell line, respectively. Immunohistochemistry analysis revealed that decreased Beclin‑1 expression was significantly correlated with poor differentiation, lymph node metastasis, advanced clinical tumour‑node‑metastasis stage, and a poor prognosis in patients with OTSCC. The in vitro assays indicated that the overexpression of Beclin‑1 significantly inhibits the proliferation and clonogenicity of OTSCC cells. These results demonstrate that Beclin‑1 acts as a tumour suppressor in the development or progression of OTSCC and that Beclin‑1 may represent a novel prognostic marker for patients with OTSCC.