Positron emission tomography (PET) can detect tumor by estimation of glucose metabolism of tumor cells. We experienced the case of intraperitoneal metastatic hepatocelluar carcinoma (HCC) diagnosed by PET. 36 year-old male patient had undergone hepatic resection for HCC. In the course of postoperative follow up, AFP level had risen gradually. We checked the abdominal sonography, CT, and celiac angiography, but results were unrevealing. To investigate hidden metastatic tumor, PET was performed and small tumor on the side of spleen was detected. The tumor was removed by laparoscopic operation, and revealed as HCC. AFP level gradually returned to normal.