In the present study, the utilization of protozoan selenium（Se）synthesized in the rumen of sheep was investigated in mice using the rate of Se incorporation into the blood, organs and tissues as an index. Protozoan Se was prepared from rumen content of sheep supplemented Na selenite（０．４mg/kg DM of diet）. Twenty female mice（over８-week-age）were divided two groups of１０each, and ten of them fed the diet containing rumen protozoa matter（rpm:１００g Se/kg DM）during consecutive７days, and another １０mice were dealt with as control group. Then, all the animals were slaughtered to collect whole blood, kidney, liver, pancreas, spleen, lung, heart, brain and muscles for analyzing Se. The Se contents in protozoa and bacteria in the rumen of sheep supplemented Na selenite（０．４mg/ Kg DM）was０．４５mg /Kg DM and０．２０mg/ Kg DM, respectively. In the concentration of Se in blood, organs and tissues, the values tended to higher in mice fed rpm diet than in control group. The Se contents in blood, organs and muscles also tended to high in the group fed rpm diet compared with that in control group. From these findings, it can be obviously concluded that the protozoan Se incorporated in the rumen is efficiently utilized in animals.