Novel composites of iron oxide encapsulated in macroporous silica with excellent arsenic adsorption performance have been successfully developed. Macroporous silica foams with large pore sizes of approximate to 100 nm and a high pore volume of 1.6 cm(3) g(-1) are chosen as the porous matrix. Electron tomography technique confirms that -Fe2O3 nanoparticles with an average particle size of approximate to 6 nm are spatially well-dispersed and anchored on the pore walls at even a high -Fe2O3 content of 34.8 wt%, rather than forming aggregates inside the pores or on the external surface. The open large-pore structure, high loading amount, and the non-aggregated nature of -Fe2O3 nanoparticles lead to increased adsorption sites and thus high adsorption capacities of both As (V) and As (III) without pre-treatment (248 and 320 mg g(-1), respectively). Moreover, the composites can reduce the concentration of both As (V) and As (III) from 100 to 2 g L-1. It is also demonstrated that the composites can be applied in a household drinking water treatment device, which can continuously treat 20 L of wastewater containing As (V) with the effluent concentration lower than the World Health Organization standard.