A 53-year -old man underwent $^{18}F$-FDG whole body PET/CT because of the detected liver mass on abdominal CT. The PET/CT showed a huge liver mass ($9{ imes}9cm$, SUV: 12.12 ) in the right lobe and a focally hypermetabolic lesion in the right lower quadrant of abdomen (SUV: 9.12). At first, we suspected that the focal hypermetabolic lesion in RLQ was the physiologic uptake of ureter or a metastatic lesion of small bowel. We repeated the abdominal PET/CT next day. The focally hypermetabolic lesion was identified as the appendiceal mass. He underwent right hemicolectomy and right lobectomy of the liver. It was confirmed that the lesion was appendiceal adenocarcinoma with liver metastasis. Cancer of the appendix is an uncommon disease that is rarely suspected before surgery. But, we suggest that PET/CT is useful to identify the small lesion like appendiceal malignant mass.