The present disclosure provides a thermoplastic copolymer composition capable of improving low noise properties without deterioration in mechanical properties, which is used in manufacture of a molded article, such as a constant velocity joint boot used as a component of an automobile. The composition includes a polyester elastomer; additives including silica and a siloxane-based polymer represented by Chemical Formula 1; and polytetramethylene glycol, where the additives are included in an amount of 1 to 4 parts by weight based on 100 parts by weight of the polyester elastomer