Background & Aims: Contrast enhanced ultrasonography (CEUS) with Sonazoid is effective for liver metastasis because enhance defect in Kupffer imaging is well delineated. The aim of this study is to investigate the detection ability of CEUS and the utility of Sonazoid in RFA for metastasis liver tumors. Material & Methods: From January 2007 to December 2007, a total of 346 liver metastatic nodules in 87 patients (62 colon cancer, 13 breast cancer, 3 gastric cancer, 3 islet cell tumor, and 6 others) admitted to receive RFA were studied. The detection ability of liver metastasis was compared between CEUS and conventional US using enhanced CT as reference standard. The mean numbers of treatment session of RFA were compared between patient treated with CEUS assistance and historical controls matched for size and number of tumors. Results: The detection rate was 78.6% with conventional US and 96.4% with CEUS (P=0.0004). 83 nodules in 25 patients were not detected by conventional US and detected after injection of Sonazoid. In addition, 12 nodules in 2 patients were detected not by CT but only by CEUS. The mean number of session was 1.5±0.5 as compared to 2.0±1.0 in the historical controls (P<0.001). Conclusions: CEUS with Sonazoid is useful for detection of liver metastasis. Sonazoid is an excellent supportive agent in RFA of liver metastasis.