To provide a graft copolymer composition expected to be useful as a modifier for improving birefringence, chemical resistance, fluidity, and the like of polycarbonate resin and the like, an adhesive between polycarbonate resin and the like and another resin, a compatibilizer between polycarbonate resin and the like and another resin, and the like.

The graft copolymer composition is obtained by graft polymerization of an alicyclic polyester-based polymer and a vinyl copolymer. The content of the segment derived from the alicyclic polyester-based polymer based on the total amount of the segment derived from the alicyclic polyester-based polymer and the segment derived from the vinyl copolymer is 25 to 99 wt.%. The content of the segment derived from the vinyl copolymer based on the total amount of the segment derived from the alicyclic polyester-based polymer and the segment derived from the vinyl copolymer is 1 to 75 wt.%.