Abstract: The distribution and accumulation of rare earth elements in mice were determined by means of counting the radioactivity of ~(169)Yb and ~(141)Ce, which were added as tracer of R. E. in the diet or injected into the veins of mieeo In the feeding experiments, more than 97％ amount of R. E. was excreted, only a small amount of ytterbium was accumulated in bone and muscle, while cerium principally in muscle. The results of injection into veins showed that most of ytterbium was distributed in liver, spleen and bone, and cerium concentrated in the same tissues except bone. On the basis of above experiments, a protein binding ytterbium or cerium was extracted from liver of mice, and a molecular weight of 61000 was determined.