A nanocomposite is prepared by encapsulating silica nano-spheres with polymerized ionic liquid in aqueous medium without use of any organic solvents. Vinyl groups are covalently introduced on to the surface of silica nano-spheres, which are then encapsulated by copolymerization of 1-vinyl-3-ethylimidazolium bromide (monomer) and 1,4-butanediyl-3,3'-bis-l-vinylimidazolium dibromide (cross-linker) at room temperature. The derived nanocomposite, PIL@SiO2, provides a green adsorbent for protein sorption. PIL@SiO2 is selective toward acidic proteins, and its selectivity can be controlled via varying the amount of monomer used in the copolymerization process. At pH 6.0, use of 5 mg PIL@SiO2 nanocomposite results in a sorption efficiency of up to 95 % for 200 mg L(-1) ovalbumin in 1 mL sample solution. Electrostatic and hydrophobic interactions between PIL@SiO2 and protein species dominate the adsorption process. The ovalbumin adsorption behavior is consistent with the Langmuir model, giving a sorption capacity of 333.3 mg g(-1). The retained ovalbumin is recovered by elution with 0.2 % SDS solution. Circular dichroism spectra reveal virtually no change to the α-helix content of ovalbumin after elimination of SDS by use of dialysis. In summary, high-purity ovalbumin is isolated from chicken egg-white by use of the PIL@SiO2 nanocomposite as adsorbent.