In this study, silica functionalized with ammonium molybdate phosphate (AMP) impregnated in calcium alginate (SiO2-AMP–Cal-Alg) was developed for the highly efficient removal of radioactive cesium from aquatic media. During the synthesis, a compact protective interlayer of silica was deliberately constructed to stabilize the AMP. The optimum composition of the SiO2-AMP–Cal-Alg beads was evaluated as 6% AMP modified SiO2 loaded into 4% calcium alginate. Because of high ion exchange capacity of the AMP functional layer, the SiO2-AMP–Cal-Alg has high removal efficiency (>91%) of radioactive cesium from 137Cs spiked solutions (3000–35 000 Bq L-1) and contaminated seawater. Batch experiments revealed that adsorption equilibrium was rapidly achieved within 30 min and the maximum sorption capacity was up to 37.52 mg g-1. Kinetic models and adsorption isotherm equations (Langmuir/ Freundlich) were used to fit the experiment data for describing the sorption process. These SiO2-AMP– Cal-Alg beads are proposed to hold great promise for the clean-up of radiocesium contaminated water around nuclear facilities after nuclear accidents.