We studied the effect of a lactic acid bacterial additive on the quality of silage made of grass-legume mixtures in the forest steppe zone of Mongolia. A high quality silage can be obtained applying a fermented liquid additive prepared on the basis of the pure cultures of lactic acid bacteria. It affects positively on the silage quality by increasing the lactic acid content relative to the total organic acid concentrations by 26.8% and decreasing acetic acid content by 19.2 percent, which led to the improved acetic acid:lactic acid ratio, and it also increases protein by 4.4 g per 1 kg fodder compared to control.