We report the use of nanospheres prepared by coating silica with molecularly imprinted polymer (MIP) for sulfamethoxazole (SMO). The resulting SiO(2)-SMO-MIP nanoparticles have highly improved imprinting and adsorption capacity, and can be used for separation and determination of sulfonamides in eggs and milk. In the synthesis, monodispersed SiO(2) nanoparticles (Si-NP) of diameter 80 nm were amino-modified by reaction with 3-aminopropyltriethoxylsilane. The acryloyl monolayer was then grafted onto the amine-modified Si-NP. Finally, the MIP films were coated on to the surface of Si-NP by the copolymerization of the vinyl end groups with functional monomer (acrylamide), cross-linking agent (ethylene glycol dimethacrylate), initiator (azo-bis-isobutyronitrile), and template molecule (sulfamethoxazole). The resulting SiO(2)-SMO-MIP-NP were characterized by transmission electron microscopy, scanning electron microscopy, and Fourier transform infrared spectrometry. The adsorption properties were demonstrated by equilibrium rebinding experiments and Scatchard analysis. The results showed that the binding sites of the SiO(2)-SMO-MIP were highly accessible, and the maximum adsorption capacity of the SiO(2)-SMO-MIP for SMO was 20.21 mg g(-1). The selectivity of the SiO(2)-SMO-MIP-NP obtained was elucidated by using SMO and structurally related sulfonamides. The results indicated that the SiO(2)-SMO-MIP had significant selectivity for SMO. The feasibility of removing SMO and sulfadiazine (SDZ) from food samples was proved by use of spiked milk and eggs. A method for the separation and determination of trace SMO and SDZ in milk and egg samples was developed, with recoveries ranging from 69.8% to 89.1%.