ABSTRACT: Aggressive properties of groundwater were studied by the authors with the emphasis on their kind and degree. Limit values of the Slovak standard no. STN 73 1215 were used as comparative values. Basic data consisted of 16 359 analyses of natural waters in which values pH and contents of Mg2+, NH, Ca+ Mg (temporary hardness), S042- and aggressive CO2 were analysed. Six types of different groundwater aggressiveness were distinguished. The analysis resulted in delineation of 22 areas. Only in two of them groundwater with non-aggressive properties were identified. For the most of the area of the Slovak Republic presence of aggressive groundwater is typical. The main parameter of aggressiveness estimated by data analysis is aggressive CO2 occurring practically in the whole territory. Presence of sulphatic aggressiveness is typical for mountainous areas and for areas with intensive agricultural activity.