A resin composition is provided. The resin composition includes a styrene-acrylonitrile based copolymer of 75 parts by weight to 90 parts by weight and rubber particles of 10 parts by weight to 25 parts by weight. The resin composition includes an oligomer trimer. The oligomer trimer includes at least one monomer unit selected from the group consisting of a styrene based monomer unit and an acrylonitrile based monomer unit. Wherein, a residual acrylonitrile based monomer is less than 5 ppm of the total weight of the resin composition. The ratio of the peak area of acetophenone to the peak area of air for the resin composition as analyzed by a thermal desorption gas chromatography mass spectrometer (TD-GC-MS) is 100 to 300.