The objective of the research study was to determine the oenological parameters of microbiologically de-acidified wines. Marechal Foch and Frontenac, young red wines, and Seyval Blanc, a white wine were the subject of the study; the wines studied were de-acidified using a starter culture of Viniflora Oenos (Oenococcus oeni). Prior to de-acidifying the wines and after it, the following was analysed: content of ethanol, total and volatile acidity, content of polyphenols; moreover, the antioxidant activity and profile of volatile compounds were determined. An attempt to reduce the excess acidity of the Frontenac wine failed. The Oenococcus oeni strains used for de-acidification caused the total acidity of the Marechal Foch wine to decrease by 28 %, and of the Seyval Blanc wine to decrease by 12 %. It was proved that the volatile acidity increased in all the wines studied (in Marechal Foch by 69 %, in Frontenac by 20 %, and in Seyval Blanc by 95 %). It was found that the antioxidant activity increased in all the wines analyzed, and the content of total polyphenols increased only in the red wines after malolactic fermentation. In all the wines analyzed, O. oeni caused the content of ethyl acetate to increase and the contents of isobutyl acetate and ethyl hexanoate to decrease. The analyses performed proved that O. oeni had a limited usefulness in de-acidifying cool climate wines with a high total acidity and a high content of alcohol.