PURPOSE: To obtain a thermoplastic resin excellent in environmental stress cracking resistance, heat stability, and layer stability, by polymerizing a mixture containing a vinyl cyanide monomer and an aromatic vinyl monomer in the presence of both a diene rubber latex and a specified acrylic rubber latex.

CONSTITUTION: A thermoplastic resin is produced by emulsion-copolymerizing 30W95wt% mixture containing a vinyl cyanide monomer and an aromatic vinyl monomer in the presence of both 4W70wt% (in terms of solids) diene rubber latex and 0.5W50wt% (in terms of solids) acrylic rubber latex. Said acrylic rubber latex is one in which the acrylic rubber is a homopolymer or copolymer of an acrylate ester monomer, has a glass transition point ≤20°C, a solubility parameter within the range of 8.9W9.5(cal/cc)1/2, and a gel content ≤70wt%.