A 80-year-old female was referred to our hospital for hematomesis. An abdominal CT revealed a heterogeneous giant tumor of about 11 cm, rich in vascularity, extending from the gastric fundus, beyond the upper side of the spleen, to the left thoracic diaphragm. Gastroscopy showed a 5 cm submucosal tumor with a visible vessel at the gastric fundus. After biopsy was performed, she was diagnosed with a c-kit-positive gastrointestinal stromal tumor (GIST)of the stomach. Following endoscopic hemostasis for gastric bleeding, imatinib mesilate was administered. The tumor reduced markedly, and vascularity in the tumor was diminished, the visible vessels of the tumor disappeared. For curative resection, total gastrectomy with a distal pancreato -splenectomy and a left diaphgram resection is necessary, but surgery was high-risk for this patient because she was advanced in age. She is now achieving a good partial response without surgery.