The aim of the present study is to investigate the effects Saccharomyces cerevisiae (Yea-Sacc 1026/Alltech) yeast culture on humoral and cellular immunity of Jersey cows in early lactation. Twenty Jersey cows in the second lactation period were equally divided to control and study groups. Starting from the 45th day of the lactation period, 10 g day(-1) of S. cerevisiae (Yea-Sacc/All-Tech Co.) were administrated to cows for 21 days. Blood were collected via vena jugularis on the 45, 52, 59, 66, 73th days postpartum. From the smears obtained, T and B lymphocyte numbers were recorded and in blood sea Bovine IgG, Bovine IgG,, Bovine IgG(2), Bovine IgM and Bovine IgA levels were deteected. In conclusion, the results of this study indicated an immunstimulant tendency of Saccharomyces cerevisia at 10 g daily in. take for dairy cows in early lactation.