Monodisperse poly(styrene-co-divinylbenzene) [P(St-DVB)] microspheres were prepared by the precipitation polymerization of styrene (St) and divinylbenzene (DVB) in acetonitrile (ACN). Effect of St/DVB ratio and monomer concentration on morphology and particle size was investigated. Monodisperse 4.1 gm P(St-DVB) microspheres were chloromethylated with chloromethyl methyl ether (CMME) and hypercrosslinked using anhydrous FeCI3 as a catalyst to form a very fine porous structure and to introduce reactive chloromethyl groups in the resulting product denoted as HC-P(St-DVB) particles. The hypercrosslinked microspheres were then functionalized with amino groups to yield HC-P(St-DVB)NH2 particles and iron oxide was precipitated within their pores. The obtained microparticles were highly magnetic with iron content similar to 38 wt% Fe. The surface of the magnetic microspheres was newly hydrophilized with methoxy-poly(ethylene glycol) (methoxy-PEG) which was confirmed by ATR FT-IR spectroscopy. The poly(ethylene glycol) (PEG)-modified magnetic microspheres were investigated in terms of sorption of serum proteins under different conditions and compared with the sorption on neat magnetic HC-P(St-DVB)-NH2 particles. The surface modification of magnetic microspheres significantly minimized the adsorption of the serum proteins. (C) 2013 Published by Elsevier B.V.