Cerium oxide (CeO 2 ) nanoparticles of size 3-5 nm and surface area 257 m 2 g 21 were synthesized using simple, single-pot, and surfactant-free aerogel process. Efforts were made to tune the surface area and porosity of CeO 2 nanoparticles by changing the concentration of precursors. CeO 2 nanoparticles were characterized by TEM, SEM, XRD, N 2 -BET, and FTIR. Prepared CeO 2 was used to remove As(III) and As(V) from water at variable contaminant concentrations (25-100 ppm) and pH (3-10). The adsorption process found extremely fast for the first few minutes of exposure. CeO 2 nanoparticles indicated adsorption capacities of 71.9 and 36.8 mg g 21 against As(III) and As(V), respectively. The adsorption data best fitted with Redlich-Peterson model, depicting monolayer adsorption. The adsorption followed pseudo-second-order kinetics and intraparticle diffusion with three-step diffusion process. The effect of co-existing anions (H 2 PO 2 4 , SO 22 4 , and HCO 2 3 ) indicated 80-96% reduction in adsorption capacity.