To provide an expandable filler composition which can be used for the reinforcement of a car body, wherein the composition maintains sufficient viscosity in the foaming temperature region and has compatibility with epoxy resins and impact resistance introduced by a crosslinked structure.

The expandable filler composition comprises 100 pts.wt. of an epoxy resin (A) derived from bisphenol A and/or bisphenol F, 1-100 pts.wt. of a thermoplastic elastomer (B) which contains a diene copolymer having an epoxy group in the main chain, has an aromatic vinyl content of 15-70 wt.%, has an oxirane oxygen concentration of 0.3-5.0 wt.% and has a number average molecular weight of 25,000-200,000, 1-30 pts.wt. of a thermally-activated curing agent (C), 0.5-100 pts.wt. of a thermally-decomposed foaming agent (D) and 3-150 pts.wt. of an inorganic filler (E).