Objective: To investigate the effects of selenium enriched yeast on antioxidative activities and immune functions in pregnant dairy cows. Methods: Twenty-four healthy Holstein-Friesian dairy cows were used for the experiment. All of them were pregnant as comfirmed by rectal palpation and divided into 4 groups, of which 3 were assigned for test groups(TI, T2, T3) and one served as control (C). Three different selenium (Se) sources namely Se-yeast (Sel Plex50, from Alltech ), mixture of Se compounds (70% Sel Plex 50 + 30% Na selenite ) and Na selenite were respectively supplemented to 3 test groups. Whole feeding experiment lasted for 168 days. During the experiment, the blood GSH-Px activity, serum Se concentration, erythrocyte superoxide dismutase(SOD) activity, malonaldehyde(MDA) level in serum, lymphocyte transformation rate and T cell count were determined. Results: Blood GSH-Px ,serum Se concentration and erythrocyte SOD activity,T1, T2 and T3 were higher (P