Ester hydrolysis at oilwater interface by lipase covalently immobilized on ionic liquid-modified magnetic nanoparticles was investigated. Magnetic supports with a diameter of 1015 nm were synthesized by covalent binding of ionic liquids (chain length C4 and C8 and anions Cl-, BF4-, and PF6-) on the surface of Fe3O4 nanoparticles. Lipase was covalently immobilized on Fe3O4 nanoparticles using ionic liquids as the coupling reagent. Ionic liquid-modified magnetic nanoparticle-grafted lipase preferentially located at the oilwater interface. It has higher catalytic activity than its native counterpart. A modified MichaelisMenten model was used to elucidate the effect of stirring rate, aqueousorganic phase ratio, total amount of enzyme, and ester chain length. The influences of these conditions on esters hydrolysis at oilwater interface were consistent with the introduction of the ionic liquids interlayer. Ionic liquids could be used to control the oilwater interfacial characteristics during lipase catalyzed hydrolysis, and thus control the behavior of immobilized lipase. (C) 2011 American Institute of Chemical Engineers AIChE J, 2012