The aim of the study was the evaluation of the biological, chemical and microbiological composition of maize silage. Changes in the amount of the ochtratoxin A and zearalenone during maize fermentation process and subsequently after a week long oxygen exposure of the silage (stability evaluation) were evaluated. The experimental material comprised maize variety Celux S.C. (FAO 220), with a dry matter content of 37% which was ensiled after cutting in the following variants (3 microsilos each). The treatments were as follows: A - control maize without additives; B - maize + 0.25% chemical additives (55% HCOOH, 5% C₂H₅COOH, 24% NH₄COOH, 1% ester of benzoic acid, 1% benzoic acid, E-151 dye), C - maize + 0.2% bacterial additives (Lactobacillus plantarum CFU 10⁶ g⁻¹, endo-1.4-beta-glukanase, xylanase, gluco-amylase). After 12 weeks of ensiling the quality of the silage, microbiological analysis, and pH value were determined. Moreover, the same analyses were carried out for the silage which underwent the 7-day oxygen exposure. The experimental preparations KemiSile 2000 and Lactacel L improved the air stability of silages, constraining the increase of the number of Clostridium, coli group and mould fungi. In most of the examined silages the mycotoxins were not detected; however, the presence of zearalenone was found in the control silage.