A differential diagnosis of liver tumors was made on the basis of the pattern of blood flow within and around tumors on color Doppler flow images. The study comprised 47 patients with liver mass lesions; 22 patients had hepatocellular carcinoma (HCC), 15 had hemangiomas, 4 had metastatic liver cancers, 3 had liver abscess, 3 had liver cysts. Color Doppler flow imaging and Doppler flow velocity were established and compared according to the Tanaka classification. Color Doppler flow imaging was observed in masses of all of 22 patients with HCC, of 3 patients with liver metastasis, of 3 patients with hemangiomas. Doppler signals were not observed in 1 patient with liver metastasis, in 3 patients with liver abscess, in 3 patients with liver cysts. The mean of maximum blood flow velocity was 80.7 cm/s in HCC, 49.3 cm/s in metastatic liver cancers, 10.3 cm/s in hemangiomas. A basket pattern (a fine blood-flow network surrounding the tumor nodule) was observed in 17 (77%) of the 22 HCC. An image of vessels within the tumor blood flow that runs into and branches within the tumor was observed in 5 (23%) of the 22 HCC. These two findings were observed only in HCC. In three of 15 hemangiomas, a spot pattern (color-stained dots or patches in the central region, of the tumor) was seen. When the blood flow wave pattern was examined, constant leaves could be seen in 6 cases (27.4%), the blood flow also showed pulsating waves in 16 (73.6%) cases with HCC. According to these results, HCCs have some characteristic appearances on color Doppler flow images. Therefore color Doppler ultrasonography can aid in the differential diagnosis of liver mass lesions.