The present invention provides a graft copolymer comprising (A) a seed comprising units derived from an alkyl methacrylate monomer; (B) a core formed on the seed and comprising units derived from an alkyl acrylate monomer; and (C) a shell formed on the core and comprising units derived from one or more one or more selected from the group consisting of an aromatic vinyl-based monomer, a vinyl cyanide-based monomer and an alkyl methacrylate monomer, wherein an average particle diameter of the core is 40 to 90 nm, and a graft ratio of the shell is 10 to 30%, and a thermoplastic resin composition and a thermoplastic resin molded article including the same.