PURPOSE: The titled composition, obtained by blending a rubber-modified styrene based resin composition containing an organopolysiloxane with glass fibers, having improved heat resistance, mold releasability and sliding characteristic and suitable for the automotive field, etc.

CONSTITUTION: A composition obtained by mechanically blending (A) 50W95wt% rubber-modified styrene based resin composition prepared by incorporating (A2) 0.25W1.25pts.wt., expressed in terms of silicon, organopolysiloxane expressed by the formula (R is alkyl, etc.; R' and R" are phenyl or 1W6C alkyl, etc.; m is a natural number), e.g. polymethylphenylsiloxane, etc., in (A1) 100pts.wt. rubber-modified styrene based resin obtained by polymerizing a mixture containing 3W15wt% rubber-like polymer dissolved in 97W85wt% styrene based monomer with (B) 50W5wt% glass fibers having 0.5W10mm length in a molten state.