Thermoplastic resin composition, method of preparing the same, and molded article including the same

A method of preparing a thermoplastic resin composition, comprising preparing pellets by kneading and extruding 100 parts by weight of a base resin consisting of 30 to 50% by weight of a (meth)acrylic acid alkyl ester compound-conjugated diene rubber-aromatic vinyl compound-vinyl cyanide compound graft copolymer and 50 to 70% by weight of a (meth)acrylic acid alkyl ester compound-aromatic vinyl compound-vinyl cyanide compound non-graft copolymer, 8 to 15 parts by weight of a polyether-amide block copolymer, 0.2 to 0.9 parts by weight of a metal stearate, and 0.001 to 0.006 parts by weight of an organic pigment under conditions of 200 to 300° C. and 100 to 300 rpm,

• wherein the graft copolymer is a graft copolymer comprising 30 to 70% by weight of conjugated diene rubber having an average particle diameter of 150 to 450 nm, 20 to 40% by weight of a (meth)acrylic acid alkyl ester compound, 5 to 20% by weight of an aromatic vinyl compound, and 1 to 15% by weight of a vinyl cyanide compound, and
• the non-graft copolymer is a copolymer comprising 60 to 80% by weight of a (meth)acrylic acid alkyl ester compound, 15 to 35% by weight of an aromatic vinyl compound, and 1 to 15% by weight of a vinyl cyanide compound.