The aim of this study was to determine the effect of different proportions of Medicago media Pers. in mixtures with Dactylis glomerata L. on the yield and nutritional value of green fodder. Qualitative analysis of fodder included the determination of the concentrations of acid detergent fibre (ADF) and neutral detergent fibre (NDF), and the relative feed value (RFV) which combines feed intake with digestibility and supports an effective evaluation of roughage. A small-area field experiment was conducted in 2010-2012 at the Agricultural Experiment Station owned by the University of Warmia and Mazury in Olsztyn (Poland). The experiment was established on mineral soil of quality class IVa and very good rye complex. The percentage of alfalfa seeds in the mixture was 30, 50 and 70% relative to the total mass of seeds of pure-sown species. Control treatments were pure-sown alfalfa (100%) and pure-sown cocksfoot (100%). The research showed that the percentage of alfalfa in yield of the mixtures was different from the relative shares of sown seeds. In the second year of the study the percentage of alfalfa was from 57 to 59% of the mass of yield. Yielding was variable among the years of research. In the first year, mixtures and pure-sown cocksfoot gave better yield than alfalfa. During the second year, the highest dry matter yield was obtained from the mixture with 70% alfalfa seeds, while the yield of pure sown cocksfoot was the lowest. Introduction of hybrid alfalfa as a component of mixtures with cocksfoot had a beneficial effect on dry matter intake by animals and increased the nutritive value of the feed.. The percentage of alfalfa seeds in the mixture differentiated the relative nutritional value of obtained feed only to slight degree.