The growing dye pollution has become an urgent threat to environmental and biological safety. To meet the requirements of both dye adsorption and photocatalytic degradation in complicated wastewater environments, here, a novel La(OH)(3)-immobilized alginate/polyacrylamide composite hydro- gel (La(OH)(3)@SA/PAM) is fabricated by in situ growth of La(OH)(3) on the inner walls of alginate/polyacrylamide networks. Because of the binding sites provided by alginate, La(OH)(3) nanoparticles are immobilized with homogeneous distribution in the hydrogel support. Notably, La(OH)(3)@SA/PAM exhibits extremely high adsorption capacities of 1610.34, 993.29, and 3000.08 mg/g for methylene blue, crystal violet, and malachite green, respectively, and the adsorption process fits the Langmuir adsorption isotherm and pseudo-second-order rate equation. The H-bonding and electrostatic interactions account for the dye adsorption. Additionally, the La(OH)(3)@SA/PAM hydrogel exhibits high photodegradation efficiency against dyes under UV-light irradiation, revealing the complete elimination of the pollutants. Furthermore, the dyes adsorbed by the hydrogel can be regenerated by solution elution. These results indicate that La(OH)(3)@SA/PAM is a promising adsorption material and an effective catalyst in wastewater purification.