The standard treatment for refractory oral chronic graft versus host disease (GVHD) has not been established. We present a case of AML accompanied by oral chronic GVHD in a 55-year-old man after allogeneic stem cell transplantation. The stomatitis of the patient was prolonged for a year and resistant to standard immunosuppressant therapy, including systemic administration of prednisolone and tacrolimus; however, local injection of 0.2% dexamethasone (0.5 mg per cm2) into the ulcerative area was drastically effective in improving refractory mucositis and mitigated a vicious cycle of mucosal damage and poor oral hygiene.