We herein describe a rare case of gastric cancer that was treated with chemotherapy during pregnancy. A woman in her thirty's at 23 weeks of gestation was admitted to the hospital with epigastralgia and left cervical lymph node swelling. She had been previously diagnosed with metastatic adenocarcinoma at another hospital. Findings from a CT scan and esophagogastroduodenoscopy revealed progressive gastric cancer, and the pathology indicated poorly differentiated adenocarcinoma. Chemotherapy was administered at 24 weeks of gestation, without the development of severe toxicity. At 32 weeks of gestation, a healthy baby girl (birth weight 1,442 g, Apgar score 7/8) was delivered by caesarean section. The child continued to show no abnormalities at 12 months after delivery.