A thermoplastic resin, wherein the thermoplastic resin is a graft copolymer having a seed-shell structure and comprises a bimodal seed comprising a large-diameter rubbery polymer having an average particle diameter of greater than 2,000 Å and 3,500 Å or less and a small-diameter rubbery polymer having an average particle diameter of 500 Å to 2,000 Å; and an aromatic vinyl-vinyl cyan polymer shell enclosing the seed, wherein the vinyl cyan compound is comprised in an amount of 5 % by weight to 15 % by weight based on a total weight of the aromatic vinyl-vinyl cyan polymer shell, wherein the graft copolymer having a seed-shell structure comprises (a) a seed comprising a conjugated bimodal diene-based rubbery polymer; and (b) a shell enclosing the seed and prepared by polymerizing an aromatic vinyl compound, a vinyl cyan compound, and fatty acid dimer or a metal salt thereof, wherein the thermoplastic resin has a graft density (σ), represented by Mathematical Equation 1 below, greater than 0.12 and 0.80 or less: σ = g d Dρ P N A 6 Mg wherein gd is a graft rate (%) calculated according to Mathematical Equation 2 below, D is an average particle diameter measured by a light scattering method, ρ is a density value of butadiene rubber particles measured according to ASTM D792, pP represents a large-diameter PBL of 0.94 g/cm3 and a small-diameter PBL of 0.97 g/cm3, NA is Avogadro's constant, and Mg is a molecular weight measured by GPC after dissolving a dried form of a sol, separated from a supernatant by a sol-gel separation method, in a TFT solution and is within 20,000 to 150,000 g/mol: Graft rate = Weight of grafted monomers g / weight of rubber g X 100 wherein the weight of the grafted monomers is (a weight of a precipitate remaining after sol-gel separation (g)) - (a weight of a rubber (g)), and the weight of the rubber is a theoretical solid weight of added rubbery polymer (g)). wherein the graft copolymer having a seed-shell structure comprises (a) a seed comprising a conjugated bimodal diene-based rubbery polymer; and (b) a shell enclosing the seed and prepared by polymerizing an aromatic vinyl compound, a vinyl cyan compound, and fatty acid dimer or a metal salt thereof, wherein the thermoplastic resin has a graft density (σ), represented by Mathematical Equation 1 below, greater than 0.12 and 0.80 or less: σ = g d Dρ P N A 6 Mg wherein gd is a graft rate (%) calculated according to Mathematical Equation 2 below, D is an average particle diameter measured by a light scattering method, ρ is a density value of butadiene rubber particles measured according to ASTM D792, pP represents a large-diameter PBL of 0.94 g/cm3 and a small-diameter PBL of 0.97 g/cm3, NA is Avogadro's constant, and Mg is a molecular weight measured by GPC after dissolving a dried form of a sol, separated from a supernatant by a sol-gel separation method, in a TFT solution and is within 20,000 to 150,000 g/mol: Graft rate = Weight of grafted monomers g / weight of rubber g X 100 wherein the weight of the grafted monomers is (a weight of a precipitate remaining after sol-gel separation (g)) - (a weight of a rubber (g)), and the weight of the rubber is a theoretical solid weight of added rubbery polymer (g)).