Disclosed is a process for producing a grafted polycarbonate resin for optical use, which comprises adding to an aqueous suspension of an aromatic polycarbonate resin having radical-polymerizable unsaturated terminal group on a molecule wherein the aromatic polycarbonate resin has an average particle diameter of 0.1 to 5 mm and an apparent density of 0.2 to 0.9 g/cm.sup.3, a vinyl monomer and a radical-polymerization initiator, heating the aqueous suspension at a lower temperature by 5.degree. C. to 20.degree. C. than the decomposition temperature for a half-life period of 10 hours of the radical-polymerization initiator, thereby impregnating the polycarbonate resin with the vinyl monomer and the radical-polymerization initiator, then elevating the temperature to the range of from a lower temperature by 50.degree. C. to a higher temperature by 30.degree. C. than the decomposition temperature for a half-life period of 10 hours of the radical-polymerization initiator, thereby conducting a graft-polymerization reaction to obtain 90% by weight or more of conversion of vinyl monomer.