The aim of the study was to investigate the effects of nano selenium (N-Se) supplementation on some metabolik parameters and rumen fermentation in sheep. In the study, twenty female Dorper sheep, average 60.1±0.44 kg of body weight were used and blood samples and rumen fluid were taken at the end of trial. The animals were randomly divided into two trial groups (n=10). The control animals received the basal ration without Se supplementation, containing a native Se content of 0.06 mg/kg DM. The other sheep were fed the same basal ration supplemented with 3 g/head/day N-Se. Trial were 66 days with 10 days of adaptation to feed and 56 days of feeding period. Serum total protein and albumin levels did not change by feeding N-Se (P>0.05). Serum T-cholesterol, triglycerides, AST (P