Disclosed is an impact-resistant thermoplastic resin composition comprising (a) a graft copolymer (II) prepared by polymerizing a monomer or monomer mixture predominantly comprised of methyl methacrylate and/or styrene in the presence of an agglomerated rubber copolymer (I') latex, and (b) bent-resistant rigid thermoplastic resin (III) comprised of .alpha.-methylstyrene or a maleimide compound. The agglomerated rubber copolymer (I') is prepared by emulsion-polymerizing an alkyl acrylate/1,3-butadiene mixture, and then agglomerating the resulting rubbery copolymer. The agglomeration is effected by adding (a) an acid group-containing copolymer prepared by emulsion polymerizing an alkyl methacrylate/unsaturated monomer mixture, and/or (b) an oxy acid salt selected from alkali metal, alkaline earth metal, zinc, nickel and aluminum salts of oxy acids having as the center element an element selected from elements belonging to the second and third periods of groups IIIA through VIA of the Periodic Table.