A 55-year-old man complained of abdominal distention. Gastroscopy showed a submucosal tumor in the upper-third portion of the stomach, with a biopsy diagnosis of gastrointestinal stromal tumor(GIST). Because abdominal contrast- enhanced CT findings suspected the invasion of the tumor into the pancreatic tail, preoperative imatinib therapy was performed. After 2 weeks of treatment, the tumor had shrunk to 44% of its starting volume. Six months later, CT findings suggestive of the tumor invasion had disappeared. Therefore, the laparoscopic local resection of the stomach was performed. The postoperative course was uneventful. A pathological diagnosis was c-kit-positive GIST, with less than 5/50 HPF of mitotic counts. Imatinib was restarted 2 weeks after the operation. The patient is alive 8 months after the operation, with no obvious recurrence. Preoperative imatinib therapy can be a useful option for large GIST tumors.