In the region of Hrvatsko zagorje there are a lot of spa localities. The study area is in the northern Pannonian part of Croatia which is characterized by a high geothermal gradient (0.049 °C/m) and surface heat flow (76 mW/m^sup 2^). Although there are a lot of thermal occurrences in the study area, only ten were taken into consideration because there was a lack of geochemical data at other locations. The thermal springs considered are: Harina Zlaka, Krapinske toplice, Tuheljske toplice, Stubicke toplice, Sutinske toplice, Semnicke toplice, Toplicica (Maðarevo), Toplicica (Gotalovec), Podevcevo, Vrazdinske toplice. A compilation of geochemical data from different sources together with our own measurements has been used in this study. The aim of this paper is to review the thermal waters' geochemical characteristics and demonstrate how these features can be used to discern their origin and the aquifer they equilibrated with. The geochemical characteristics of thermal waters of the study area suggest that the water is in equilibrium with dolomite which means that dolomite is the thermal aquifer in the study area.