A process for preparing an impact resistant resin, which comprises a step of graft copolymerizing a monomer mixture comprising an aromatic vinyl monomer and a monomer copolymerizable therewith, to a butadiene rubber-like polymeric latex in the presence of a redox polymerization initiator; a step of coagulating the resulting graft copolymer latex by mixing an antioxidant thereto and adding an alkaline earth metal salt thereto; and a step of washing the coagulated product by a washing water having the pH adjusted to a level of at most 7.