Gastrointestinal stromal tumors are characterized by the expression of CD34 and c-kit (CD117) and represent the most common mesenchymal malignancy of the gastrointestinal tract. Imatinib mesylate is small molecule tyrosine kinase inhibitor that suppresses transmembrane receptor c-kit products. Clinical studies for metastatic and inoperabl GISTs have demonstrated partial response rate ranging from 40% to 69% in patients treated with imatinib mesylate. But complete response is rare. We present a 46 year old man patient with unresectable gastrointestinal stromal tumor that has histopatologically proven complete response to imatinib mesylate therapy.