Corn silage with 36.5 % of average dry substance was included in the experiment, for check without additive (K0) and for experiment with chemical preservative containing potassium sorbate, sodium benzoate and sodium nitrite (Safesil) in a dosis of 1 l/t chopped whole plant (D1) and 3 l/t (D3). The chopped whole plant was ensilaged at the farm at Netluky in a bag with diameter of 2.7 m on 26.9.2010. The ensilage analyses were made in April (after sample taking by a probe) and in August 2011 (after opening the bag). There were no significant differences between the variants in the contents of dry matter and nutrients. The pH values were 4.12 for K0 silage, 4.23 for D3, respectively; the contents of lactic acid was 4.4 vs. 4.0 %, acetic acid 2.6 vs. 3.0 %, alcohol 6.3 vs. 2.5 %. The K0 ensilage stayed stable only 19 hours when its temperature rose by 3°C (according to Honig methodology). The D1 ensilage had aerobic stability by 18 hours longer than K0 and by 3 hours shorter than D3. The temperature of the ensilage D1 rose up to the level of K0 (32°C); D3 did not show such an intensive increase; so the total energy losses in the sum of temperatures were distinctively lower for D3 than for D1 and K0. The tested agent can be recommended for restriction of aerobic degradation of corn silages.