Use of ultrasonography (US) in diagnosing liver tumors has advanced with improvements in B-mode, color Doppler, and contrast enhancement methods. Similarly remarkable advances in three dimensional technology achieved during the past ten years are expected to find clinical use soon. Further, striking progress is also being made in CT and MRI technology. The importance of US is made unshakable, however, by its minimal invasiveness, high spatial and time resolution, and low cost. Because diagnosis of liver tumor is the most important role for US, sonographers should strive to gain up-to-date knowledge of its application. In this review, we explain the differential diagnosis of such tumors as hepatocellular carcinoma, intrahepatic cholangioma, metastatic liver tumor, hemangioma, focal nodular hyperplasia (FNH), and liver adenoma.