ABSTRACT: Research results of the groundwater chemical composition from Neogene volcanic rocks of Slovakia focused on sulphates and sulphur isotope contents is presented in the paper. The research was done by members of the Department of Hydrogeology in the period 2004 – 2006. Groundwater from 12 sources (springs, mining works, and well) was sampled and analyzed. Evaluation of sulphate and sulphur isotope contents was complemented by statistical assessment of 1919 groundwater analyses coming from Neogene volcanic rock environment as used for compilation of the Geochemical atlas of Slovakia, part Groundwater. The results showed that the groundwater of Neogene volcanic rocks has a typical chemical composition in which sulphates play an important role. Sulphates sulphur isotope research showed that its value in all analyzed sources belongs to the range of values typical for sulphur of volcanic origin, or for sulphur of sulfides bound to rock of volcanic origin, respectively.