This study was designed to evaluate the effects of dietary mannan oligosaccharide (MOS) and Saccharomyces cerevisiae (SC) in finishing turkeys' diets on performance, intestinal microflora, duodenal viscosity and pH, and blood constituents. A total of seventy-two, Big6, 10-week-old, male poults were divided into three dietary treatments and eight replicate pens per treatment. Treatments including the following: 1. basal diet (control - C, no additive), 2. addition of MOS 1 g per kg basal diet, and 3. SC 1 g per kg (strain SC47, 300 x 10(10) CFU/kg) basal diet. The treatments did not affect body weight, duodenal viscosity, and pH. The daily feed intake (P<0.01) and feed conversion ratio (P<0.05) in the MOS group were higher than those of the control and SC groups. The ileum total bacteria, gram negative bacteria and E. coli counts in the SC group were lower than those of the control and MOS groups (P<0.05). The serum triacylglycerols, cholesterol, HDL, LDL, glucose, total protein, albumin, globulin, and creatine concentration of turkey toms were not influenced by the dietary MOS and SC supplementation (P>0.05).