To introduce thiol-ene chemistry in the modification of composites by ionic liquid (IL), a novel functional IL, 1-methylimidazolium mercaptopropionate (MimMP), was synthesized and investigated as a modifier for styrene-butadiene rubber/silica composites. MimMP could be hydrogen-bonded with silica and react with the double bonds of rubber chains via thiol-ene chemistry. The filler networking, curing behavior, filler dispersion, crosslink density, and mechanical performance were fully studied. The filler networking in the uncured rubber compounds was effectively restrained. The vulcanization was largely accelerated by MimMP. The interfacial interaction was quantitatively evaluated and found to consistently increase with increasing MimMP. The mechanical performance and abrasion resistance of the modified vulcanizates improved considerably. The remarkable improvements were mainly ascribed to the improved interfacial structure comprised of MimMP-silica hydrogen bonding and MimMP-rubber covalent bonds via thiol-ene chemistry. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1252-1260, 2012