The bioavailability of incorporated Se from bacteria and protozoa collected from rumen of sheep was investigated using female Wistar rats to simulate the lower digestive tract of a ruminant. The rats were fed diets supplemented with different sources of Se, namely: control – without Se, ISe – with selenite, PSe – with protozoan Se, BSe – with bacterial Se. After a 7-day feeding trial, blood samples were collected through the abdominal aorta and all animals were slaughtered for organ and tissue samples. The Se absorption and retention in PSe or BSe was almost similar to that in ISe, although the variation was quite high in microbial Se. The whole-blood Se level in BSe and PSe was similar, though numerically higher in PSe than BSe. Se levels in the liver and kidney also tended to be higher in ISe than in PSe or BSe. The results suggest that microbial Se can be efficiently utilized, although bacterial Se is more available and comparable to selenite in terms of retained Se relative to what is absorbed. Se from protozoa appeared to be less available than selenite, as judged by the smaller amount of Se in some organs of rats fed PSe than in those in the ISe group.