In 2004-2005 means were sought to clean grain from microbiological contamination during transportation and storage. For this purpose, grains with a moisture content of 23.2% of the “Tauras” variety were selected and ventilated daily for 8 hours until grain wetness was reduced to 14.0%. The effect of ventilation duration and ozone impact was evaluated according to the changes in grain contamination with micromycetes propagules (cfu · g^-1), and alternation of micromycetes species on the grain surface. At drying grains by active ventilation with an ozone – air mixture, at O₃ concentration of 700 ppb, the drying period was reduced by about 20%, and mycological contamination depends on initial grain moisture content (w): when w=15.2%, contamination was reduced by up to 2.2 times, and when w=22.0% – up to 3 times. At the same time, the composition of micromycetes species on the grain surface changed significantly: in non-ventilated grain there were detected micromycetes of 26 species, and in ventilated grain – of 11 species. Efficient ozone impact was established only when the mound of wet (w>18.0%) grains was exposed to ozone.