Maize silage is the main conserved roughage used in animal feed in Brazil and improving its quality has great relevance. The aim of this experiment was to evaluate the characteristics of maize silage, containing different percentages of soybean biomass. In this way, different percentages of soybean green biomass added to maize ensilage (0, 10, 20, 30 and 40%-experiment 1 and 0, 10, 20, 30, 40 and 50% in experiment 2) were evaluated. Experiments were laid out as a completely randomized. Variables were submitted to analysis of variance and when it present significance was applied regression analysis. Silage ashes increased as soybean biomass increased. Regarding to the neutral and acid detergent fiber and the amount of total digestible nutrients, there was no effect of the treatments. At experiment 1, silage crude protein increased from 7.5 to 12.6% from sole maize silage to the silage with 39.2% of soybean dry biomass, which represent an increase of 67.24%. At experiment 2, it increased from 6.77 to 12.09%, which represent 78.58% more protein at the treatment with 50% of soybean green biomass (41% dry matter of soybean) in relation to the sole maize silage. At experiment 2, for every 1% increase in soybean dry matter biomass addition, there was an increase of 0.1% of maize silage crude protein. The addition of soybean biomass to corn silage increases the ashes and crude protein content of silage.