The main purpose of this work was to determine adsorption characteristics of heavy metal cations on two Slovak bentonites. Adsorption of Pb²⁺, Zn²⁺, Cu²⁺ and Cd²⁺ on Jelsovy Potok (JP) and Lieskovec (L) bentonites was studied by the batch equilibration technique using solutions of different concentrations. Higher smectite content (81 mass %) and higher cation exchange capacity (CEC) (105 mmol M⁺/100 g) of JP bentonite cause higher adsorption of all heavy metals in comparison with L bentonite. JP adsorbed heavy metals in the order Pb²⁺>>Cd²⁺>Zn²⁺>Cu²⁺ while sorption on L was slightly different, Pb²⁺>>Cd²⁺>Cu²⁺ ≥ Zn²⁺. The Freundlich model of adsorption is more appropriate for adsorption of Pb²⁺ and Cd²⁺ while lower uptake of Cu²⁺ and Zn²⁺ is better described by the Langmuir model. Negative ΔG° values indicate that the adsorption process of all cations on both bentonites is feasible, spontaneous and exothermic. The decrease in the d001 spacings from 14.8–14.9 Å in natural dominantly Ca²⁺-saturated samples to 13.2–12.6 Å for both bentonites saturated with four heavy metal cations shows the effect of less hydrated exchangeable cations on interlayer spacing. Jelsovy Potok bentonite of higher montmorillonite content and greater CEC is the more effective candidate for removal of Pb²⁺, Zn²⁺, Cu²⁺ and Cd²⁺ from waste water than Lieskovec bentonite.