Molecularly imprinted polymers (MIPs) were grafted from the surface of Fe3O4 nanoparticles containing double bond via suspension polymerization in aqueous environment, and the leakage of Fe3O4 nanoparticles from MIPs was overcome in this study. The effect of different cross-linker on adsorption capacity of the resultant magnetic MIPs was investigated using pure trimethylolpropane trimethacrylate (TRIM) or the mixture of TRIM and divinylbenzene (DVB) as cross-linker. Both magnetic MIPs exhibited higher adsorption capacity for the template theophylline than the corresponding non-imprinted polymer, and Freundlich model fitted reasonably well for theophylline adsorption on both magnetic MIPs. In addition, both magnetic MIPs exhibited good recognition properties for the template theophylline versus caffeine, and the selectivity of magnetic MIPs using pure TRIM as cross-linker (mag-MIP-TRIM) was much higher than those using the mixture of TRIM and DVB as cross-linker (mag-MIP-TRIM and DVB). The adsorption dynamics of theophylline on both magnetic MIPs fitted well with the first-order kinetic model, but the adsorption equilibrium on mag-MIP-TRIM and DVB reached faster than that on mag-MIP-TRIM. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:1930-1937, 2011