The present invention is related to a method of manufacture of a graft copolymer latex and its dried powder including a step of manufacture of a latex using a reactive surfactant for a surfactant in manufacturing of the graft copolymer latex containing acrylic polymers and a step of manufacture of dried powder in which the graft copolymer latex manufactured in the above step of manufacture of a latex is sprayed and dried. The method according to the present invention is effective in that it is possible to provide for dried powder of a graft copolymer latex having a low moisture content and a high powder density and to provide for a thermoplastic resin composition containing the above latex having superior luster, tensile strength, and thermal stability.