To evaluate the glucose metabolism in the liver tumor, 18FDG PET (Positron Emission Tomography) was performed in 9 patients with primary and metastatic liver tumors. And usefulness of 18FDG PET in clarifying the effect of treatment on liver tumor was examined. Glucose metabolism of tumor was showed in terms of the coefficient 'C' calculated by Patlak's plot. Each tumor's coefficient 'C' was 0.016-0.054 and it decreased after treatment. Compared with pathological findings, the coefficient 'C' of necrosis part of tumor was 0.004 and fibrous change after irradiation was 0.007. It suggested that coefficient 'C' reflected activity of tumor and it was a useful index to know viability of tumors in the treatment for patients with liver tumors.