Background: This study aimed to evaluate the usefulness of Sonazoid enhanced radiofrequency ablation under real-time virtual sonography (RVS) guidance in a series of patients with hepatocellular carcinoma (HCC). Method: Twenty-five patients with a solitary HCC tumor measuring < = 2.5 cm in greatest dimension were enrolled in this study. Eight patients received an initial treatment, seven also received an additional treatment for local recurrent tumors, and the remaining ten had distant recurrent tumors. All patients were easy to scan by multiple detector CT (MDCT), but not by conventional ultrasound ( Conclusions: The combination of the RVS system with Sonazoid-enhanced US appears to have a high potential for use on patients that are difficult-to-scan by US examinations for percutaneous radiofrequency ablation. Background & Aims: Contrast enhanced ultrasonography (CEUS) with Sonazoid can be expected to be useful not only for detection of tumor but also for US guided ablation therapy because Kupffer imaging lasts for long time. The aim of this study is to investigate the usefulness of Sonazoid in RFA for HCC. Material & Methods: A total of 716 HCC nodules in 316 patients admitted to receive RFA were studied. The detection ability of HCC was compared between CEUS and conventional US using dynamic CT as reference standard. The effectiveness in the treatment was assessed by comparing the mean numbers of treatment session of RFA in patient treated with CEUS assistance and that in historical controls matched for tumor and background conditions. Results: The detection rate was 83.5% in conventional US and 93.2% in CEUS (P=0.04). Sixty-nine nodules in 52 patients were not detected by conventional US and detected after injection of Sonazoid. The mean increase in detected tumor number with contrast enhanced US were well correlated with serum albumin level (P=0.016). CEUS was not superior to conventional US in patients with low albumin level. The mean number of session was 1.33±0.45 as compared to 1.49±0.76 in the historical controls (P=0.0019). Conclusions: CEUS with Sonazoid is useful for detection of tumor in patients with well-conserved hepatic reservoir. The decrease in the mean number of sessions compared to historical controls suggested that Sonazoid is an excellent supportive agent in RFA treatment of HCC. 