Abstract:Actinomycosis is a specific inflammatory disease that shows typical symptoms of trismus, plate-like induration, and multiple abscess formation. However, it has recently become difficult to diagnose because of a decreased number of cases show typical symptoms. A 85-year-old woman was referred to our clinic because of swelling with left molar region and trismus. Radiographic examination revealed bone destruction and lysis of the mandible. Although a malignant tumor was suspected, the histopathological diagnosis was actinomycosis. Surgical curettage was performed, and Benzylpenicillin and Amoxicillin was administerated.