There is disclosed a thermoplastic resin composition wherein the dispersion of a polyorganosiloxane in a thermoplastic resin is improved by the inclusion of a copolymer of an organosiloxane compound and an ester of a vinylcarboxylic acid or a copolymer of an aromatic vinyl compound, an unsaturated aliphatic nitrile compound and an organosiloxane compound. As a consequence of the excellent dispersion, the composition has improved moldability compared with conventional thermoplastic resins containing only polyorganosiloxane and yields moldings that have a releasability, lubricity, water repellency and mechanical strength superior to moldings from the conventional thermoplastic resins containing only polyorganosiloxane.