PURPOSE: To evaluate the amount and patterns of the vascularity of liver tumors and to assess the usefulness in the differentiation of liver tumors with power Doppler ultrasound (US). MATERIALS AND METHODS: Forty patients with liver tumors (27 hepatocellular carcinomas (HCCs), 7 cholangiocarcinomas, and 6 metastases) were prospectively evaluated with power Doppler US. Liver tumors were confirmed by biopsy or proved by dynamic CT and angiography with transcatheter arterial chemoembolization. The amount of Doppler signal was classified as absent; moderate, and marked and the pattern of intratumoral Doppler signals was classified as central, peripheral, and diffuse. RESULTS: Overall, power Doppler US showed absent (18%), moderate (43%), and marked (40%) and the pattern of Doppler signals was central (35%), peripheral (23%), and diffuse (25%). In HCCs, all cases were moderate (56%) or marked (44%) and the most frequent pattern of Doppler signals was central (35%). In cholangiocarcinomas, power Doppler US showed absent (43%), or marked (57%) Doppler signals were 67% and 33%, respectively, and one was central (17%) and the other was peripheral (17%) pattern. CONCLUSION; Power Doppler US is sensitive in detecting Doppler signals and is useful in evaluation of the vascularity within liver mass. Also Power Doppler US is expected to help to differentiate various liver tumors.