Positron emission tomography/computed tomography (PET/CT) examinations are indispensable in determining the stage, evaluating the treatment response, and diagnosing recurrence and metastasis during oral cancer treatment. In this study, we examined the correlation between the maximum standardized uptake value (SUVmax) for 18F-FDG PET/CT and the progressive factors, biological characteristics, and prognosis of oral cancer. We included 52 cases of oral squamous cell carcinoma with surgery as the initial treatment. Inclusion criteria included tumor diameter of ≥ 1 cm excluding superficial cancer. We performed 18F-FDG PET/CT examinations before surgery and determined the correlation between SUVmax and clinicopathological factors, such as histological grade, Ki-67 expression, as well as progress factors. SUVmax was significantly correlated with clinical T stage, vascular invasion, lymphatic invasion, Ki-67 expression, and postoperative event (recurrence or metastasis) in Student's t test. Using a cut-off SUVmax of 8.0, clinical T stage, lymph node metastasis, vascular invasion, infiltrative pattern, and Ki-67 expression significantly correlated in chi-squared test. Although observed and expected 3-year overall survival rates were not significantly different, observed and expected 3-year disease-free survival rates were significantly different. Analyzing each clinicopathological factor using various data obtained from 18F-FDG PET/CT scans may be useful to determine prognosis during oral cancer treatment.