The frequency of rectal gastrointestinal stromal tumor (GIST) is relatively low. We have experienced three cases of giant rectal GIST. Case 1 was treated with sunitinib after imatinib failed by Stevens-Johnson syndrome as neoadjuvant therapy. Case 2 was treated with imatinib as neoadjuvant therapy. These neoadjuvant therapies had no effect on tumor size. All patients underwent an abdominoperineal resection. The mean major axis was 11 .7 cm. Immnohistochemical staining showed that CD34 and KIT were positive. The term of follow-up is short, but no recurrences have been found in all cases. It has been reported that imatinib as neoadjuvant therapy is useful for radical resection in cases of giant rectal GIST. Furthermore, neoadjuvant therapy seems to be one of the treatment options for locally advanced rectal GIST. However, in cases of GIST patients not responding to imatinib, we should perform a surgical resection immediately.