This investigation was carried out in order to study the effect of Saccharomyces cerevisiae and malt sprout byproduct effects on afshari fattening lambs. The experiment was conducted using fourty afshari males lambs with average body weight of 26± 5 kg and 90± 10 day age in a completely randomized design with four treatments. After two weeks of adaptation, the lambs were fed for eighty days with balanced rations formulated according to NRC (1984) recommendations. The applied treatments were:1) barley group (Control group) 2) malt group 3) barley group including of Saccharomyces cerevisiae 4) malt group including of Saccharomyces cerevisiae Lambs were weighted every weeks before morning feeding. For measuring blood parameters, five lambs were randomly selected in each treatment and blood samples were collected from jaugular wein of the lambs four hours after morning feeding. Lambs fed diets with malt sprout byproduct significantly increased (p 0.05) DM intake, daily live weight gain but there were not significantly differences among treatments for feed conversion ratio. Supplementation of diet with live yeast and malt sprout byproduct did not affects (p 0.05) blood parameters such as glucose, Blood urea nitrogen, Aspartate aminotransferase, Albumin, alb/glb, White blood cell, Lymphocyte, Neutrophil, Monocyte, Eosinophil but were found differences among treatments in Red blood cell, Glubulin and Total protein. then generally it can be concluded addition of malt sprout byproduct to improved growth performance and in turn, immune system of lambs but their interaction with live yeast did not affect on growth performance and blood parameters related on immune system. Keywords : Saccharomyces cerevisiae yeast , immune system, growth performance, malt sprout by product