The aim of the study was to analyze the mycobiota occurring on the grapes originating from Slovak wine-growing regions. The main focus was to discover the presence of the representatives of the genus Alternaria on/in grape berries and in the stum.Using the direct method of placing grape berries on the culture medium was analyzed their total and endogenous (after superficial sterilization) mycobiota. Plate dilution method was used for stum mycobiota determination. Alternaria spp. colonized grapeson the surface and inside with anisolation frequency (Fr) of 100%. Moreover, 100% of the stum samples were positive for the presence of this genus. Their relative density (RD) was 44.9% (unsterilized grapes), 57.9% (sterilized grapes) and 6.35% (stum). In all the areas analysed we recorded 4 species-groups: A. alternata, A. arborescens, A. infectoria and A. tenuissima. With the highest Fr and RD occurredA. tenuissima species-group, followed by A. alternata and A. arborescens species-groups. All of them are potential producers of mycotoxins as alternariol, alternariol monomethylether, tenuazonic acid, altertoxin I, II and III.