The aim of the experiment was to find the effect of two different yeast strains Saccharomyces cerevisiae ? Sc 47 a Sc 1020), supplemented to the concentrate mixture for dairy cows, on dry matter intake (DMI), milk production and milk composition. The animals were divided into two experimental (Sc 47 ? B, Sc 1020 ? L) and one control (K) groups. The highest DMI was detected in the K group. The yeast supplements increased milk yield significantly as well as the celulolytic activity of rumen liquid. Simultaneously, the milk fat concentrations and ? in the case of group B ? milk protein concentration were decreased.