Oral squamous cell carcinoma (OSCC) is very common in Taiwan and most patients with high adverse factors will receive adjuvant radiotherapy or chemotherapy after surgery. Rad51 is a well known DNA repair protein and serves a central role in homologous recombination. Rad51 overexpression has been reported in several different types of cancer and served as an inferior prognostic marker. Therefore, the aim of the study is to determine the role of Rad51 in oral cancer.