Mixtures of selected species of microorganisms including predominant populations of lactic acid bacteria, photosynthetic bacteria, yeasts, actinomycetes and molds, have been effectively used recently and have gained attention worldwide for sustainable agriculture (improving soil quality, soil health, and the growth, yield, and quality of crops), and to a lesser extent, in animal production systems. Two effective microorganisms (EM) solutions, control fermented solution (EM-U) or fermented solution with added sugarcane molasses, (EM-A) were evaluated as additives for ensiling sorghum (Sorghum bicolor) harvested during the end of summer season in Catalonia, Spain. The inoculant (EM) was mixed (% of fresh wt) with the chopped grass (H2 cm particle size) to form four treatments: 1) Control (No EM); 2) EM-A2 (EM-A inoculant applied at 2%); and 3) EM-A5 (EM-A at 5%); and 4) EM-U2 (EM-U at 2%). For each treatment, duplicate plastic bags were lled with 20 kg of fresh chopped sorghum, adequately compacted and stored at ambient temperature in the dark. After 2.5 months incubation, the two bags per treatment were emptied and sampled in order to determine ef uent pH, DM, and volatile fatty acids (VFA) and ammonia nitrogen (NH3-N) concentrations. Statistical analysis of data was performed with PROC GLM of SAS. Effective microorganisms improved (P < 0.05) fermentation characteristics of silages, decreasing pH and NH3-N, and increasing VFA concentrations. There were signi cant differences (P < 0.05) between the doses for the evaluated parameters; lowest pH (4.05) was obtained with EM-A2, while no differences were detected for NH3-N and VFA between the two extended treatments (EM-A2 and EM-A5). Control and EM-U2 treatments did not differ in DM (18.36 vs. 18.12%) or VFA (107.04 vs. 127.60 mmol/l) concentrations; however, pH and NH3-N were decreased with EM-U2, which was considered the optimal treatment in this study.