NOVELTY - A thermoplastic resin composition comprises (in parts mass) heat-resistant acrylic resin (100), rubber-containing copolymer particles (0.1-50) and thermostabilizer (0.1-10). The heat-resistant acrylic resin includes methacrylate and/or acrylate unit (40-90 %mass), aromatic vinyl compound unit (5-40 %mass) and dione repeating unit (I) (5-30 %mass). The rubber-containing copolymer particles have average particle diameter of 0.04-0.13 mu m. The difference in the refractive index of rubber-containing copolymer particles and heat-resistant acrylic resin is 0.015 or less.    USE - Thermoplastic resin composition is used for molded product e.g. polarizing plate protecting film and retardation film for optical medium (all claimed). Uses include but are not limited to bumper, lens, optical fiber, touch panel, rear projection television, waveguide, optical exchange system, solar cell, headlamp and front grille.    ADVANTAGE - The thermoplastic resin composition has excellent optical characteristics, heat resistance, mechanical strength and processing stability.    DETAILED DESCRIPTION - A thermoplastic resin composition comprises (in parts mass) heat-resistant acrylic resin (100), rubber-containing copolymer particles (0.1-50) and thermostabilizer (0.1-10). The heat-resistant acrylic resin includes methacrylate and/or acrylate unit (40-90 %mass), aromatic vinyl compound unit (5-40 %mass) and dione repeating unit of formula (I) (5-30 %mass). The rubber-containing copolymer particles have multilayer structure with average particle diameter of 0.04-0.13 mu m. The difference in the refractive index of rubber-containing copolymer particles and heat-resistant acrylic resin is 0.015 or less.    X=O or N-R;and    R=hydrogen, alkyl, aryl or cycloalkyl.    INDEPENDENT CLAIMS are included for the following:    (1) molded product, which contains thermoplastic resin composition; and    (2) manufacture of thermoplastic resin composition, which involves mixing heat-resistant acrylic resin, rubber-containing copolymer particles and thermostabilizer.