In this study, we characterized the physical properties of bentonite colloids, conducted stability tests, and examined the effects of the colloids on the sorption of radionuclides in groundwater (Cs-137). The resulting data provides a valuable reference for safety assessments of final disposal sites for spent nuclear fuel and high-level radwaste. Our results demonstrate that Cs-137 is easily adsorbed by bentonite colloids. Adsorption capacity of colloidal solutions was shown to be greater than that of colloidal gel type, and the adsorption rate decreases with an increase in ionic strength in a groundwater environment.