<p>Biopolymer modification offers an environmentally friendly approach to enhance the retention performance of bentonite toward radionuclides. This study used bentonite as the adsorption matrix, while xanthan gum (XG) and guar gum (GG) were incorporated in a comparative framework to systematically investigate their impacts on Sr²⁺ adsorption behavior and underlying mechanisms. Batch adsorption experiments were conducted to evaluate the effects of biopolymer content, initial Sr²⁺ concentration, contact time, and pH of the solution. The results show that both XG- and GG-modified bentonite exhibit significantly enhanced Sr²⁺ uptake compared to unmodified bentonite, with optimal contents of approximately 1.5% for XG and 0.5% for GG. At low Sr²⁺ concentrations, adsorption is primarily governed by ion exchange. As the Sr²⁺ concentration increases, exchangeable sites gradually approach saturation, and non-exchange contributions become increasingly important. The adsorption of Sr²⁺ remains stable under neutral to weakly alkaline pH conditions. Microstructural characterization indicates that biopolymer modification does not alter the mineral composition or crystal framework of bentonite but enhances Sr²⁺ adsorption by regulating the external surface and interfacial adsorption environment. Among the investigated systems, XG-modified bentonite exhibits a more pronounced enhancement effect than GG-modified bentonite. These findings provide mechanistic insight into biopolymer-regulated Sr²⁺ adsorption on bentonite and highlight the potential of modified bentonite for radionuclide immobilization in engineered barrier and environmental applications.</p>