We elucidated the features of the time-related contrast-enhanced ultrasound appearance of hypervascular liver tumor using Definity, which has no accumulation activity in the liver. Ten rabbits with VX2 tumors broadcast into the liver were used. Changes in contrast-enhanced sonograms were evaluated by real-time observation (FR 15 Hz) of harmonic imaging under extra-low MI (MI 0.065) with Definity, and their intensity changes were analyzed. Hepatic angiography (4/10) and histopathological examination (10/10) were performed to investigate the tumor vascularity. VX2 tumors were hypervascular on angiogram (4/10) and histology (10/10). They showed time-related sonographic appearance changes from hyperechoic to hypoechoic, which were confirmed by quantitative intensity analysis. Hypervascular VX2 tumors showed characteristic time-related shift on contrast-enhanced sonograms in real-time and extra-low MI harmonic images with Definity. These findings may be useful for the ultrasound diagnosis of human hypervascular liver tumor like hepatocellular carcinoma with blood-pool contrast agent.