The aim of this thesis was to determine how the application of ectomycorrhizal mycelium to the root of grapevine affects the chemical composition of wine 'Portugieser'. The experiment was set up in fall 2016. in 3 locations in the area of ZOI Plešivica, when the application of vaccine called „Mykoflor” of a company named Bio-budućnost d.o.o. from Zagreb was also performed. The vaccine was applied to 100 vines of variety 'Portugieser', with the same number of vines serving as a control. Analysis of chemical composition of wine was carried out after the harvest in 2018. at Department of Viticulture and Enology of Faculty of Agriculture in Zagreb in accordance with the O.I.V. (2001.) methods. By High Performance Liquid Cromatography (HPLC), single polyphenolic compounds were determined according to Tomaz and Maslov (2016.) method. Also, sensory evaluation of wine was performed using the method of 100 positive points. The results showed favorable effect of mycorrhiza on chemical composition of wines obtained from infected vines compared to the control wines. Positive effect was manifested in higher concentration of acids, sugar, increase in ash content and lower pH values. Application of mycorhizza also had a positive effect on the polyphenolic composition of wine.