ABSTRACT: Sulphate anions represent a substantial part of groundwater chemical composition in the underground hydrologic system of the Krásnohorská jaskyňa Cave and its surroundings. Basic sulphate component, as defined here (SO4 2- of ~20.7 mg∙L-1, δ34SSO4 ~6.24 ‰ and δ18OSO4 of ~4.08 ‰), is possibly formed by sulphates of bacterial origin on the ground surface and snow cover. Basic sulphate component is present in groundwater elsewhere around the area in all groundwater sources. In its “pure form”, without presence of sulphates from other sources, it was detected in several groundwater sources. Quantitative majority of sulphates dissolved in water of the underground hydrologic system of the Krásnohorská jaskyňa Cave is probably bound to Lower to Middle Triassic sediments (probably Szin Member), where the supposed original δ34S value is about ~28.86 ‰. In the cave, this was the especially case of the tributary from the Helictite Dome. At various places, in various ratios depending on the water stage, this is then mixed with groundwater containing only basic sulphate component. Still, the water properties of the Pri kaplnke spring are so similar to that of the Buzgó spring / outflow from the cave that bifurcation of its underground flow should be considered. Other springs in broader neighbourhood with dissolved sulphates above ~20 mg∙L-1 and δ34SSO4 above ~7 ‰ can be more probably linked to Permian / Lower Triassic sediments of Perkupa Formation with δ34S of 10 ‰ to 12 ‰. To recognize this, two-component mixing curve with basic sulphate component and geogenic sulphate endmembers should be plotted in the background of specific analysis.