To develop green and reusable catalysts for the biodiesel preparation, a novel magnetically separable nanocatalyst was fabricated by covalent bonding of 3-sulfopropyl-1-(3-propyltrimethoxysilane) imidazolium hydrogen sulfate ([SO3H-PIM-TMS]HSO4) on mesoporous silica modified Fe3O4 nanoparticle. The catalyst possessed uniform core-shell structure with magnetic response core and Bronsted ionic liquid functionalized mesoporous silica shell. The multifunctional catalyst also exhibited appealing physicochemical features like high specific surface area, mesoporous channel, magnetic response, and fine catalytic activity in esterification of oleic acid with alcohol. Under mind conditions, the conversion of oleic acid was up to 93.5%. The catalyst exhibited recyclable property based on magnetism and the separation of the catalyst would be simply using external magnetic field without obvious mass loss, allowing a clean biodiesel product. (C) 2014 Elsevier B.V. All rights reserved.