A polycarbonate copolymer which comprises 30 to 70 mol % of a structural unit comprising a bisphenyl fluorene structure and 70 to 30 mol % of a structural unit comprising tricyclo [5.2.1.0.sup.2.6] decanedimethanol and causes little occurrence of a birefringence even when extrusion, injection molding or stretch processing is conducted and a process for producing the same.