The present invention relates to an acrylic rubber-modified copolymer and the styrenic thermoplastics composition using the same. More particularly, the present invention relates to the styrenic thermoplastics composition having superior appearance and thermoformability, which is obtained by adding 0.5-20 parts by weight of an acrylic rubber-modified copolymer having a rubber particle size ranging from 800 to 6, 000 Åto 100 parts by weight of a resin of 10-50 parts by weight of a graft copolymer comprising rubber-modified styrene and 30-70 parts by weight of a copolymer comprising styrene.