Investigations were carried out into the comparative assessment of yielding capacity in annual grass-and-legume crops, millet and oats, in pure sowings as well as in mixture with pea, field pea and vetch. The experiment was performed in 2011-2014 on dark-chestnut soils of the Republic of Tuva (Durgen). Under arid conditions of the steppe zone of Tuva, such grass mixtures as millet + peas and millet + field peas sown at the first date (III ten-day period of May) were remarkable among annual grass-and-legume crops for their average green mass yields during years of investigations; these were 17.7 and 16.6 tonnes per ha, respectively. At the second sowing date (II ten-day period of June), the maximum yield was observed in millet + peas mixture (19.7 tonnes per ha), and in oats + field peas mixture (19.7 tonnes per ha). There was determined the biological efficiency coefficient of annual grass-and-legumes mixtures when grown for green mass, depending on components and sowing dates. The biological efficiency of grass-and-legumes mixtures was found to be higher than that of the pure grass sowings. The maximum indices were obtained in the variants oats + field peas (1.25) and peas + oats (1.23) sown at the second date. There were determined the optimum sowing dates for annual grass-and-legume crops in the forest-steppe zone of Tuva: III ten-day period of May for fodder millet + leguminous crops (peas, field peas) mixtures, and II ten-day period of June for oats + peas and field peas mixtures.