Primary malignant lymphoma of the appendix is an unconnnon neoplasm although the gastrointestinal tract is the most common extranodal site of malignant lymphoma. We report a case of primary malignant lymphoma of the appendix in a 54-year-old male, who presented with pain in the right lower abdomen. An appendectomy was performed. The appendix measured 9.5 cm in length and 5.5 cm in diameter. Cut sections showed a solitary circumferential mass in the appendiceal lumen. Light microscopic features were compatible with malignant lymphoma of diffuse large cell type(Working Formulation) and the immunophenotype was B cell type.