A 73-year-old woman had undergone mastectomy for left breast cancer. One year later, bone metastasis was detected. After 7 years, the patient experienced epigastric discomfort, and gastrointestinal endoscopy showed stenosis of the pylorus and enlarged gastric folds. Stomach cancer was suspected at first, but gastric metastasis of breast cancer was diagnosed on the basis of endoscopic reexamination and computed tomography(CT)images. The patient could not drink water, and therefore, gastrointestinal stenting was performed, which facilitated ingestion to some extent. However, at the same time, an elevated serum carcinoembryonic antigen(CEA)level and jaundice were observed. Therefore, biliary tract stenosis due to carcinomatous peritonitis was diagnosed. We attempted to treat the jaundice with endoscopic retrograde cholangiopancreatography( ERCP)or percutaneous transhepatic cholangiography(PTCD), but the treatment was not successful, and an increase in ascites was noted. Accordingly, gemcitabine was administered as systemic therapy. As a result, ascites decreased and jaundice improved. Patients with gastric metastasis of breast cancer have poor quality of life(QOL)because of difficulties in ingestion or vomiting, and poor prognoses, because of frequent concurrent carcinomatous peritonitis. We experienced a case of gastric metastasis and carcinomatous peritonitis, and were able to improve the patient's QOL by gastrointestinal stenting and gemcitabine administration.