A case of a giant mucinous cystadenoma of the appendix presented with ileus is reported with a review of the literature. An 82-year-old woman was admitted to the hospital because of abdominal pain and frequent vomiting. After recovery of the ileus by welling an ileus tube, abdominal computed tomography revealed a 9.3×7.6cm giant mass lesion of the cecum. A colon fiberscopy revealed a submucosal tumor-like elevated lesion of the appendix orifice, but a biopsy material taken from the epithelia of appendix orifice did not reveal any abnormal findings. With s suspicion of primary tumor of the appendix, an ileo-cecectomy was carried out. The resected tumor was 10×7×6cm in size. Microscopically it was mucinous cystadenoma. The patients postoperative course was uneventful.