A tumor hemorrhage is reported to be a rare adverse reaction of imatinib mesylate in gastrointestinal stromal tumors (GIST). We encountered two patients with tumor hemorrhage under imatinib treatment. Case 1: An 18-year-old woman underwent partial gastrectomy for gastric GIST at 14 years old. She complained of abdominal pain, and intraperitoneal relapse of GIST was diagnosed. She received imatinib mesylate treatment and twice developed an abdominal hemorrhage, which on both occasions was cured by conservative therapy. We resected the GIST as best as we could and restarted imatinib mesylate. There were no hemorrhages or relapses for twenty-nine months and five months, respectively. Case 2: A 35-year-old woman had an abnormality on the upper gastrointestinal series at a medical check-up and was given a diagnosis of gastric GIST, abdominal dissemination and multiple liver metastases. She was treated with imatinib mesylate, however she suffered an intra-abdominal hemorrhage which required surgery. We resected the tumors as best as we could and restarted imatinib mesylate. We obtained a clinical complete response for forty months. We have been successful at continuing treatment with imatinib mesylate with no recurrence, suggesting the efficacy for hemorrhage from GIST caused by imatinib mesylate.