Disclosed is a lubricant for thermoplastic resins, which is prepared by (A) polymerizing 60-100 wt. % of an aromatic vinyl monomer and 0-40 wt. % of other vinyl monomer copolymerizable therewith to form a polymer, (B) polymerizing 30-70 wt. parts of a monomer or monomer mixture comprising 50-100 wt. % of an acrylic acid ester and 0-50 wt. % of other vinyl monomer or monomers copolymerizable therewith in the presence of 10-60 wt. parts of said polymer so that when said monomer or monomer mixture is singly polymerized, the reduced viscosity of the resulting polymer is lower than 1.0, to obtain a polymer, and (C) polymerizing 5-30 wt. parts of a methacrylic acid ester in the presence of the two-stage polymer obtained at the steps (A) and (B) so that the total amount of the components (A), (B) and (C) is 100 wt. parts. A thermoplastic resin composition comprising this lubricant has an excellent mold release characteristics and lubricating property at the molding step, and a molded article prepared from the composition has a good gloss.