The present study was conducted to assess the varietal and seed proportion effects on yield, quality and compatibility of oats and vetch mixtures under varying seed proportion (100%, 75%, 50%, 25%) using two varieties for each of the component species. The experiment was conducted in Randomized Complete Block Design (RCBD) with three replications. Seedling count, biomass yield, plant height, vigor and plot cover were collected. Forage quality traits considered for the experiments were DM content, ash, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, cellulose and hemicelluloses. Relative yield, Relative yield total, Relative crowding coefficient and Aggressivity index were indices calculated for biological compatibility and yield advantages of oats and vetch. Significant (P