To describe some clinical and subclinical characteristics of oral cavity cancer patients with III-IVA,B stage and to evaluate VMAT radiation plan. Materials and method: Uncontrolled clinical trials in 46 patients diagnosed with III-IVA,B stage oral cavity cancer at the Head and Neck Radiotherapy Department – National Cancer Hospital from September 2018 to June 2022. Results: The average age was 54,83 9,78 years [27-74], male patients accounted for 84,8%. The lesion was mainly located on the tongue, accounting for 47,8%, followed by the floor of the mouth, accounting for 21,7%. Pain when chewing and having cervical lymph node are two most common symptoms with the rate of 95,7% and 34,85, respectively. Stage III, IVA, IVB are 10,9%, 82,6% and 6,5%, respectively. PETCT changed the stage in 17,4% of patients. Evaluation of VMAT radiation plan: the dose into the radiation volumes and the organ at risk meet the requirements according to the recommendations. Conclusion: Oral cavity cancer stage III-IVA,B is common in middle-age men. The most common of tumor location is tongue with clinical symptoms is pain on chewing and having cervical lymph node. PETCT has a role to help accurately assess the pre-treatment stage. The VMAT radiotherapy plan met the recommend standards.