The present study was conducted with 18 lactating cows(20.5㎏ of daily milk yield) to observe effects of yeast diets on milk yield and composition. Lactating cows were slotted to one of the three diets, by completely radomized design, of the yeast culture supplemented total misted diet(YCSD), the brewer`s yeast slurry based total mixed diet supplemented with yeast culture(BY-YC) and the commercial concentrate as a control. Yeast culture was prepared by mixing of wheat bran, water and Saccharomyces cerevisiae(Gist-brocade, Delft-Halland) in the ratio of 1 : 1 : 0.0045(w/w) and fermenting this mixture for 3∼5 days at 18∼20℃. Yeast culture was then added to the pre-formulated diets at 0.5% level(DM basis) and fermented for 3 days at the same temperature as for preparing yeast culture prior to feeding. The BY-YC diet was prepared by adding yeast culture at the 50% level of YCSD to brewer`s yeast slurry(7.72%, DM basis) based total mixed diet, and then fermented for 3 days at the same temperature as for preparing yeast culture prior to feeding. The cows were fed the experimental diets including corn silages twice daily(08:00 and 16:30) based on NRC requirements(1988) with consideration of crude protein and neutral detergent fiber(NDF). The study was conducted for a total of 9 wks including 1 wk adaptation period to the diets. The results observed were summarized as follows No differences in intakes of DM and CP were observed among the sroups except that NDF intake was reltively higher for YCSD and BY-YC than for control. Cows fed YCSD revealed better milk consistency during whole period than those fed control or BY-YC. Feeding YCSD and BY-YC tended to improve daily milk yield, 4% FCM and feed efficiency compared to the control diet group while milk composition(fat, protein and lactose) were not influenced by the diets. Production of each milk components were high in the order of YCSD, BY-YC and control as influenced by milk yield. Thus overall better productions were obtained from the cows fed YCSD.