An 82-year-old woman was admitted to the hospital because of tiredness and fever. She was diagnosed with acute hepatitis. Although the cause of acute hepatitis was undetermined, her health condition and liver function improved, and she was discharged. Four weeks later, she was hospitalized again because of anorexia. Laboratory data revealed worsened anemia. Endoscopy results revealed a huge ulcerative lesion in the lesser curvature of the stomach. After 4 days, she vomited blood and died of hemorrhagic shock. The autopsy revealed a nasal-type primary gastric extranodal NK/T-cell lymphoma (ENKTL). Although no lymphoma cells were found in the liver biopsy collected during the first hospitalization, lymphoma cells and lymphocytes in the liver tissue were identified during autopsy because the lymphoma had infiltrated the liver. Primary gastric ENKTL is extremely rare and poorly understood. However, the general prognosis of progressive ENKTL is poor. Early diagnosis of liver metastasis of lymphoma cells is difficult;thus, in some cases, lymphoma metastases to the liver are diagnosed during autopsy. Although further experiments are required, we report a rare case of primary gastric ENKTL.