Abstract: Calcium carbonate nanoparticles were prepared in the presence of poly(styrene sulfonate) (PSS). The samples were characterized by scanning electron microscopy (SEM). The sorption of UO²⁺₂ onto CaCO₃ nanoparticles was investigated as a function of pH, ionic strength and temperature under ambient conditions using batch technique. The results indicate that sorption of UO²⁺₂ onto CaCO₃ nanoparticles increases with increasing pH and decreasing ionic strength. With increasing temperature, maximum adsorption of UO²⁺₂ increases. The thermodynamic data indicate that the sorption of UO²⁺₂ onto CaCO₃ nanoparticles is an endothermic and spontaneous process.