A case of actinomycosis of the stomach in a 61-year-old woman is reported. The patient presented to the hospital with a history of epigastric pain, fatigue, poor appetite, constipation and mild fever of 20 days' duration. On physical examination, a tender mass was felt at the epigastrium. Computed tomography (CT) showed a heterogeneously enhanced mass at the posterior wall of the stomach. Upper gastrointestinal series revealed a submucosal mass at the gastric antrum. A malignant tumor was suspected and surgery was recommended. A 5 x 4 x 2 cm mass was found at the posterior wall of the distal gastric antrum. A Billroth II subtotal gastrectomy was performed. Pathologic examination revealed suppuration and sulfur granules in the indurated mass. The patient was subsequently treated with intravenous penicillin-V for 12 days and then with oral penicillin-G for 4 months. She remained well at her last follow-up appointment. Although the initial radiologic findings were nonspecific, CT was of importance in delineating the location and evaluating the extent of the lesion.