Herein, we report a 39-year-old female patient presenting with gastric cancer and tuberculous peritonitis. The differential diagnosis between advanced gastric cancer with peritoneal carcinomatosis and early gastric cancer with peritoneal tuberculosis (TB), and the treatment of these two diseases, were challenging in this case. Physicians should have a high index of suspicion for peritoneal TB if the patient has a history of this disease, especially in areas with a high incidence of TB, such as South Korea. An early diagnosis is critical for patient management and prognosis. A surgical approach including tissue biopsy or laparoscopic exploration is recommended to confirm the diagnosis.