Effect of viable yeast culture (Saccharomyces cerevisiae) was studied on ruminal fermentation and total digestibility in the rumen using cannulated sheep. Four Kiviricik sheep were used in a factorial arrangement of 4x4 Latin square designs. Treatment diets used were 700g/kg alfalfa hay + 300 g/kg concentrate mix (diet I), 700 g/kg alfalfa hay + 300 g/kg concentrate mix + 4 g/day Saccharomyces cerevisiae (diet II), 700 g/kg concentrate mix + 300 g/kg alfalfa hay + 4 g/day Saccharomyces cerevisiae (diet III), and 700 g/kg concentrate mix + 300 g/kg alfalfa hay (diet IV), respectively. Nutrient intakes did not change with yeast supplementatin among the animals fed diets. Ruminal pH at 0 h was lower when sheep fed with diet III and IV compared to diet I and II. Saccharomyces cerevisiae supplementation (diet II and III) increased ruminal ammonia nitrogen (NH3-N) concentration at 4 h. However, total volatile fatty acids (VFA) concentrations were not affected with yeast supplementation, Saccharomyces cerevisiae supple-mentation did not affect nutrient digestibility of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF), and acid detergent fiber (ADF).