Hg(II) ions dissolved in aqueous solutions were adsorbed by montmorillonite (MMT). The Hg(II) ion-exchange was strongly limited by the competition with H+ ions: the maximal amounts of adsorbed Hg(II) and H+ ions were 0.21 mmol g-1 and 1.10 mmol g-1, respectively. MMTs saturated with Hg(II) (Hg-MMTs) were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and thermal analysis. Hg(II) ions, such as Hg2+ and [Hg(OH)+], along with H+ ones were mostly adsorbed on permanent sites (75 % of cation exchange capacity (CEC)) and also on pH dependent surface sites (25 % of CEC). While heating, Hg-MMTs was loosing their mass up to 700 °C as a result of the MMT dehydration and dehydroxylation accompanied by release of adsorbed Hg(II)., Petr Praus, Marcela Motáková and Michal Ritz., and Obsahuje bibliografii