Gastrointestinal stromal tumor (GIST) is a rare tumor of the digestive tract, but it is the most common of the mesenchymal tumors. The location is often gastric and small intestine. GIST of the appendix is extremely rare. We report one case in a 48-year-old man. He complained of severe pain in the right iliac region. The clinical presentation was typically like acute appendicitis. Abdominal ultrasound was performed and suspected an appendicular abscess. Surgical excision of the appendix was performed and histological diagnosis was "gastrointestinal stromal tumor of the appendix".